msm: mdss: Fix AD calibration mode resume backlight issue

AD when set in calibration mode will block all backlight
updates from frameworks. Hence during suspend/blank the
backlight would not be 0 but will be set to the value
set in calibration mode.

Now this is changed as during suspend the backlight is
set to 0 within driver itself. This complicates things by
causing backlight to remain 0 post resume in calibration
mode. Now changing the behavior so that backlight is set
to 0 during suspend and set to the calibration set value
upon resume.

Change-Id: Id0b3919a7034875b3f3a606d00f462ceb21f40ee
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>