[PATCH] cpuset: unsafe mm reference fix

Fix unsafe reference to a tasks mm struct, by moving the reference inside of a
convenient nearby properly guarded code block.

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>