backlight: extend event support to also support poll()

Extend the backlight event support to also allow the use of
poll()/select() on actual_brightness.

We already have the entire event hookup anyway, adding a single
function call in one line to get functionality like that is a really
good deal.
Signed-off-by: NHenrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: NRichard Purdie <rpurdie@linux.intel.com>

drivers/video/backlight/backlight.c

@@ -91,6 +91,7 @@ static void backlight_generate_event(struct backlight_device *bd,
 	}
 	envp[1] = NULL;
 	kobject_uevent_env(&bd->dev.kobj, KOBJ_CHANGE, envp);
+	sysfs_notify(&bd->dev.kobj, NULL, "actual_brightness");
 }
 
 static ssize_t backlight_show_power(struct device *dev,