msm: mdss: Don't calculate AD with zero backlight

Don't calculate AD strength when backlight is zero to prevent updates that
would not be visible from impacting screen when first backlight request
arrives.

Change-Id: Iabf10317ef40ae7bd940d94297a62975947c5ee4
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
1 file changed