sony-laptop: fix bogus error message display on resume

sony_backlight_update_status returns 0 on success -1 on failure (i.e.: the
return value from acpi_callsetfunc. The return value in the resume path
was broken and thus always displaying a bogus warning about not being able
to restore the brightness level.

Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Len Brown <len.brown@intel.com>