vmscan: fix comments related to shrink_list()

Fix the shrink_list name on some files under mm/ directory.

Signed-off-by: Anderson Briglia <anderson.briglia@indt.org.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>