UBIFS: introduce categorized lprops counter

commit 98a1eebda3cb2a84ecf1f219bb3a95769033d1bf upstream.

This commit is a preparation for a subsequent bugfix. We introduce a
counter for categorized lprops.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>