drm/i915: don't warn if backlight unexpectedly enabled

drm/i915: don't warn if backlight unexpectedly enabled

commit 813008cd3e93ea8a571b2b7d5b9360a3105b50f7 upstream.

BIOS or firmware can modify hardware state during suspend/resume,
for example on the Toshiba CB35 or Lenovo T400, so log a debug message
instead of a warning if the backlight is unexpectedly enabled.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80930
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>