ENGR00268508 backlight:Correct the setting for bd props.fb_blank

ENGR00268508 backlight:Correct the setting for bd props.fb_blank

The patch of "ENGR00264855 backlight: Support backlight shared by
multiple fbs" doesn't consider that bd->props.fb_blank could be
shared by several framebuffers which use the same backlight device.
This causes the pwm backlight wrongly check the fb blank status.
This patch corrects the setting for the fb blank status by
considering all the framebuffers in question to fix the issue.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
(cherry picked from commit 68b97d114629f22f64b3d8c14d0a0b7d07d6ebb2)
[shawn.guo: cherry-pick commit 8a03a96fba08 from imx_3.10.y]
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>