video: msm: Clear previous histogram data on next startup

Clear the pointer to the userspace histogram struct when histogram is
started. Previously, when the histogram was stopped while a histogram read
was in progress, the pointer was not cleared, causing the next histogram
read to think that someone was already using the histogram.

CRs-Fixed: 361640
Change-Id: If09017149e98b35c49603372c554aa4c97f2de82
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
(cherry picked from commit 19e4b71f617e307cacf0be077e08bec5c37df290)

Signed-off-by: nobodyAtall <tsogkas@ceid.upatras.gr>
video: msm: Enable mdp clock for histogram and histLUT

Enable the mdp clock for histogram and histogram LUT to ensure that the
clock remains enabled when they are being accessed.

Change-Id: Ic744f2ee96b64442f23ba19aa1c38552c0dad83a
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
(cherry picked from commit e782ceab26e38590cd49a9bb273da1dbf1984ccd)

Signed-off-by: nobodyAtall <tsogkas@ceid.upatras.gr>