mm: fix typos and grammar error in comments

We moves tha -> We move that in mm/swap.c
statments -> statements in include/linux/mm.h

Link: https://lkml.kernel.org/r/20210509063444.GA24745@hyeyoo


Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>