platform/x86: thinkpad_acpi: Use backlight helper

Instead of retrieving the backlight brightness in struct
backlight_properties manually, and then checking whether the backlight
should be on at all, use backlight_get_brightness() which does all
this and insulates this from future changes.

Signed-off-by: Stephen Kitt <[email protected]>
Cc: Henrique de Moraes Holschuh <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: Mark Gross <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Daniel Thompson <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>

drivers/platform/x86/thinkpad_acpi.c

@@ -6798,10 +6798,7 @@ static int brightness_set(unsigned int value)
 
 static int brightness_update_status(struct backlight_device *bd)
 {
-	unsigned int level =
-		(bd->props.fb_blank == FB_BLANK_UNBLANK &&
-		 bd->props.power == FB_BLANK_UNBLANK) ?
-				bd->props.brightness : 0;
+	int level = backlight_get_brightness(bd);
 
 	dbg_printk(TPACPI_DBG_BRGHT,
 			"backlight: attempt to set level to %d\n",