inotify: Do not drop mark reference under idr_lock

inotify: Do not drop mark reference under idr_lock

Dropping mark reference can result in mark being freed. Although it
should not happen in inotify_remove_from_idr() since caller should hold
another reference, just don't risk lock up just after WARN_ON
unnecessarily. Also fold do_inotify_remove_from_idr() into the single
callsite as that function really is just two lines of real code.

Reviewed-by: Miklos Szeredi <[email protected]>
Reviewed-by: Amir Goldstein <[email protected]>
Signed-off-by: Jan Kara <[email protected]>