xtensa: add missing __user annotations to __{get,put}_user_check

__get_user_check and __put_user_check use temporary pointer but don't
mark it as __user, resulting in sparse warnings:

  sparse: warning: incorrect type in initializer (different address spaces)
  sparse:    expected long *__pu_addr
  sparse:    got long [noderef] <asn:1> *ret

  sparse: warning: incorrect type in argument 1 (different address spaces)
  sparse:    expected void [noderef] <asn:1> *to
  sparse:    got long *__pu_addr

Add __user annotation to temporary pointer in __get_user_check and
__put_user_check.

Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>