mm/damon: remove unnecessary do_exit() from kdamond

Just return from the kthread function.

Link: https://lkml.kernel.org/r/20210927232421.17694-1-changbin.du@gmail.com


Signed-off-by: Changbin Du <changbin.du@gmail.com>
Cc: SeongJae Park <sjpark@amazon.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>