drm/i915: Fix inconsistent backlight level during disabled

When the brightness property is inquired while the backlight is disabled,
the driver returns a wrong value (zero) because it probes the value after
the backlight was turned off.  This caused a black screen even after the
backlight is enabled again.  It should return the internal backlight_level
instead, so that it won't be influenced by the backlight-enable state.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=41926
BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/872652

Tested-by: Kamal Mostafa <[email protected]>
Cc: Alex Davis <[email protected]>
Cc: <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: Keith Packard <[email protected]>
1 file changed