platform: x86: Deletion of checks before backlight_device_unregister()

The backlight_device_unregister() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
For msi-wmi.c:
Acked-by: Anisse Astier <anisse@astier.eu>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

drivers/platform/x86/sony-laptop.c

@@ -3141,8 +3141,7 @@ static void sony_nc_backlight_setup(void)
 
 static void sony_nc_backlight_cleanup(void)
 {
-	if (sony_bl_props.dev)
-		backlight_device_unregister(sony_bl_props.dev);
+	backlight_device_unregister(sony_bl_props.dev);
 }
 
 static int sony_nc_add(struct acpi_device *device)