msm: kgsl: Fix memory leak after snapshot

When a snapshot is taken and the objects saved in snapshot are
merged then the memory entry reference for one of the merged
objects should be returned otherwise it can leak.

Change-Id: Ie76392570e2623e6ae22619003c5fd1c58c5fb98
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>