_SHMEM=n build fix

Fix bug found by Grant Coady <lkml@dodo.com.au>'s autobuild setup.

shmem_set_policy() and shmem_get_policy() are macros if !CONFIG_SHMEM, so this
doesn't work.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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