gralloc1: Acquire mutex early in release

Due to race condition between release and retain calls, retain return stale handle.
Which results in crash in SurfaceFlinger
Fix crash by acquiring mutex early in release function

Bug: 32384569
Change-Id: I4b763bbcacd9905492d19fafc9b91e4c7e1cc53e
(cherry picked from commit 6a711d2b)