backlight: simplify lcd notifier

With all the work I've done on replacing fb notifier calls with direct
calls into fbcon the backlight/lcd notifier is the only user left.

It will only receive events now that it cares about, hence we can
remove this check.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528090304.9388-34-daniel.vetter@ffwll.ch