drm/msm/dsi-staging: fix incorrect handling of backlight config failures

For sharp wqhd dualdsi panel, panel binding gets failed due
to incorrect handling of parsed backlight configuration failures. This
change fixes the same by not returning all failures as fatal errors
in panel binding.

Change-Id: Ie5a556b896f2d6866362ae7a8c45f1f0385c2101
Signed-off-by: Tharun Raj Soma <tsoma@codeaurora.org>