mm/damon: remove unnecessary do_exit() from kdamond

mainline inclusion
from mainline-5.16
commit 5f7fe2b9
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4GVMK
CVE: NA

-------------------------------------------------
Just return from the kthread function.

Link: https://lkml.kernel.org/r/20210927232421.17694-1-changbin.du@gmail.comSigned-off-by: NChangbin Du <changbin.du@gmail.com>
Cc: SeongJae Park <sjpark@amazon.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 5f7fe2b9)
Signed-off-by: NYue Zou <zouyue3@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

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"