gpu: ion: use module_platform_driver to simplify the code

module_platform_driver() makes the code simpler by eliminating
boilerplate code.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/tegra/tegra_ion.c

@@ -81,16 +81,5 @@ static struct platform_driver ion_driver = {
 	.driver = { .name = "ion-tegra" }
 };
 
-static int __init ion_init(void)
-{
-	return platform_driver_register(&ion_driver);
-}
-
-static void __exit ion_exit(void)
-{
-	platform_driver_unregister(&ion_driver);
-}
-
-module_init(ion_init);
-module_exit(ion_exit);
+module_platform_driver(ion_driver);