percpu: add __percpu to SHIFT_PERCPU_PTR

The SHIFT_PERCPU_PTR() returns a pointer used by a number
of functions that expect the pointer to be __percpu annotated
(sparse address space 3). Adding __percpu to this makes the
following sparse warnings go away.

Note, this then creates the problem the __percup is marked
as noderef, which may need removing for some of the internal
functions, or to remove other warnings.

mm/vmstat.c:385:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:385:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:385:13:    got signed char *
mm/vmstat.c:385:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:385:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:385:13:    got signed char *
mm/vmstat.c:385:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:385:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:385:13:    got signed char *
mm/vmstat.c:385:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:385:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:385:13:    got signed char *
mm/vmstat.c:401:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:401:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:401:13:    got signed char *
mm/vmstat.c:401:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:401:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:401:13:    got signed char *
mm/vmstat.c:401:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:401:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:401:13:    got signed char *
mm/vmstat.c:401:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:401:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:401:13:    got signed char *
mm/vmstat.c:429:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:429:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:429:13:    got signed char *
mm/vmstat.c:429:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:429:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:429:13:    got signed char *
mm/vmstat.c:429:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:429:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:429:13:    got signed char *
mm/vmstat.c:429:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:429:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:429:13:    got signed char *
mm/vmstat.c:445:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:445:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:445:13:    got signed char *
mm/vmstat.c:445:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:445:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:445:13:    got signed char *
mm/vmstat.c:445:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:445:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:445:13:    got signed char *
mm/vmstat.c:445:13: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:445:13:    expected signed char [noderef] [usertype] <asn:3> *__p
mm/vmstat.c:445:13:    got signed char *
mm/vmstat.c:763:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:763:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:763:29:    got signed char *
mm/vmstat.c:763:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:763:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:763:29:    got signed char *
mm/vmstat.c:763:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:763:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:763:29:    got signed char *
mm/vmstat.c:763:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:763:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:763:29:    got signed char *
mm/vmstat.c:825:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:825:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:825:29:    got signed char *
mm/vmstat.c:825:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:825:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:825:29:    got signed char *
mm/vmstat.c:825:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:825:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:825:29:    got signed char *
mm/vmstat.c:825:29: warning: incorrect type in initializer (different address spaces)
mm/vmstat.c:825:29:    expected signed char [noderef] <asn:3> *__p
mm/vmstat.c:825:29:    got signed char *

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Dennis Zhou <dennis@kernel.org>