video: msm: Initialize HistLUT with last saved LUT

Set HistLUT to last value written to LUT when MDP is turned on. Assumes
that last LUT corresponds to last BL scale value sent.

CRs-Fixed: 475149
Change-Id: I7383666c2d1f3d8800c5f25e2ef648568eb33a74
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>