qnap-poweroff: Fix license string

GPLv2+ is not a valid license string. Replace it with one that is.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>

drivers/power/reset/qnap-poweroff.c

@@ -113,4 +113,4 @@ module_platform_driver(qnap_power_off_driver);
 
 MODULE_AUTHOR("Andrew Lunn <andrew@lunn.ch>");
 MODULE_DESCRIPTION("QNAP Power off driver");
-MODULE_LICENSE("GPLv2+");
+MODULE_LICENSE("GPL v2");