fbdev: msm: change backlight pwm config function

Use pwm_config function to update the BL value, this will
make similar to un-blank call. Calling different function
calls to update the pwm value during blank and un-blank
can cause in-appropriate behaviour.

Change-Id: I4b23e7d4c3f6bf03a1c3b8f4167264b12ae079c4
Signed-off-by: Himanshu Agrawal <hagraw@codeaurora.org>
Signed-off-by: Rajshekar Eashwarappa <reashw@codeaurora.org>
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>