msm: mdss: Update BL on first AD update

First AD update is not updating with current backlight value. Initialize
last_bl variable so that first request updates backlight along with user
specified input.

Change-Id: I453e5448229dbddb6204c0a654c267e1540c59a3
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
1 file changed