mm/damon/sysfs-schemes: handle schemes sysfs dir removal before commit_schemes_quota_goals

'commit_schemes_quota_goals' command handler,
damos_sysfs_set_quota_scores() assumes the number of schemes sysfs
directory will be same to the number of schemes of the DAMON context.  The
assumption is wrong since users can remove schemes sysfs directories while
DAMON is running.  In the case, illegal memory accesses can happen.  Fix
it by checking the case.

Link: https://lkml.kernel.org/r/20240213023633.124928-1-sj@kernel.org


Fixes: d91beaa5 ("mm/damon/sysfs-schemes: implement a command for scheme quota goals only commit")
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>