mm/memory.c: fix spello of "function"

Fix typo/spello of "function".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/e7bf180e-c558-b1d5-9a15-6d9708823c9c@infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>