Revert "msm: mdss: Prevent non-zero backlight following display blank"

Patch broke assumption that blank/unblank does not modify backlight value.
This reverts commit 3d4c5574f8284df4b29b4bdbe31fc2b6c4aef079.

Change-Id: I5dfeb0504d23089e7a9dca423726185eddb40d7e
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>