mm/damon/core: simplify the kdamond stop mechanism by removing 'done'

mm/damon/core: simplify the kdamond stop mechanism by removing 'done'

When the 'kdamond_wait_activation()' function or 'after_sampling()' or
'after_aggregation()' DAMON callbacks return an error, it is unnecessary
to use bool 'done' to check if kdamond should be finished.  This commit
simplifies the kdamond stop mechanism by removing 'done' and break the
while loop directly in the cases.

Link: https://lkml.kernel.org/r/1663060287-30201-4-git-send-email-kaixuxia@tencent.com
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>