mm/frontswap: fix some typos in frontswap.c

There are some typos in comment, fix them.

s/Fortunatly/Fortunately
s/taked/taken
s/necessory/necessary
s/shink/shrink

Signed-off-by: Ethon Paul <ethp@qq.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200411064009.15727-1-ethp@qq.com


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