mm: LKSM: bug fix for KASAN out-of-bound access error on accessing a filter

mm: LKSM: bug fix for KASAN out-of-bound access error on accessing a filter

KASAN reports out-of-bound accesses (reported by Jaehoon Chung)
on slab which is performed for obtaining a next filtered
address to find a sharable page.

LKSM exploits bitmap-based filters to find sharable pages in
an efficient way. A buggy code is a kind of miscalculation for
boundary of the allocated bitmap. This patch takes care of it.

Change-Id: If45c5ce175db067523b60f11e69e12d2bc798659
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>