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: Henrique de Moraes Holschuh <[e-mail]>
Signed-off-by: Richard Purdie <[e-mail]>

drivers/video/backlight/backlight.c

···
 	}
 	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,