msm: mdss: Fix locking errors in histogram disable

There is a histogram variable that was missing the spinlock while it
was being read. It has been added.

Change-Id: I5f6d4246332a84c6a4cb3503ad7bbfaddb4a0fa8
Signed-off-by: Benet Clark <benetc@codeaurora.org>
1 file changed