kernel/auditfilter: kill bogus uninit'd-var compiler warning

Kill this warning...

kernel/auditfilter.c: In function ‘audit_receive_filter’:
kernel/auditfilter.c:1213: warning: ‘ndw’ may be used uninitialized in this function
kernel/auditfilter.c:1213: warning: ‘ndp’ may be used uninitialized in this function

...with a simplification of the code.  audit_put_nd() can accept NULL
arguments, just like kfree().  It is cleaner to init two existing vars
to NULL, remove the redundant test variable 'putnd_needed' branches, and call
audit_put_nd() directly.

As a desired side effect, the warning goes away.

Signed-off-by: Jeff Garzik <jeff@garzik.org>