Fallout from "Remove fs.h from mm.h" patch

While I was busy compile-testing my patch, ENOSYS sneaked into pm.h
leading to some compile-breakages mostly on ia64 and some mips configs.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>