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.comSigned-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>

mm/damon/core.c

@@ -714,7 +714,7 @@ static int kdamond_fn(void *data)
 	nr_running_ctxs--;
 	mutex_unlock(&damon_lock);
 
-	do_exit(0);
+	return 0;
 }
 
 #include "core-test.h"