asus-wmi: backlight_init: Stop treating -ENODEV as if its not an error

When bl_power support got added to asus-wmi, the error handling for it was
written to ignore -ENODEV, to avoid not registering a backlight interface for
models which have no bl_power control, but do have brightness control.

At the same time the error handling for brightness_max was modified to do the
same, this is wrong, when there is no brightness_max asus-wmi should not
register a backlight interface.

Note the caller of asus_wmi_backlight_init already special cases -ENODEV,
and will not cause the wmi driver regristration to fail because of a
-ENODEV return from asus_wmi_backlight_init.

https://bugzilla.redhat.com/show_bug.cgi?id=1097436

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/asus-wmi.c

@@ -1271,10 +1271,7 @@ static int asus_wmi_backlight_init(struct asus_wmi *asus)
 	int power;
 
 	max = read_brightness_max(asus);
-
-	if (max == -ENODEV)
-		max = 0;
-	else if (max < 0)
+	if (max < 0)
 		return max;
 
 	power = read_backlight_power(asus);