mm/damon/sysfs: cleanup attrs subdirs on context dir setup failure

mm/damon/sysfs: cleanup attrs subdirs on context dir setup failure

When a context DAMON sysfs directory setup is failed after setup of attrs/
directory, subdirectories of attrs/ directory are not cleaned up.  As a
result, DAMON sysfs interface is nearly broken until the system reboots,
and the memory for the unremoved directory is leaked.

Cleanup the directories under such failures.

Link: https://lkml.kernel.org/r/20251225023043.18579-3-sj@kernel.org
Fixes: c951cd3b8901 ("mm/damon: implement a minimal stub for sysfs-based DAMON interface")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: chongjiapeng <jiapeng.chong@linux.alibaba.com>
Cc: <stable@vger.kernel.org> # 5.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>