mm/vmscan.c: fix typo

Change "optizimation" to "optimization".

Signed-off-by: dylan-meiners <spacct.spacct@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: http://lkml.kernel.org/r/20200609185144.10049-1-spacct.spacct@gmail.com


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