staging: mt7621-pci: use builtin_platform_driver()

Macro builtin_platform_driver can be used for builtin drivers
that don't do anything in driver init. So, use the macro
builtin_platform_driver and remove some boilerplate code.
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200321133624.31388-1-sergio.paracuellos@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-pci/pci-mt7621.c

@@ -725,9 +725,4 @@ static struct platform_driver mt7621_pci_driver = {
 	},
 };
 
-static int __init mt7621_pci_init(void)
-{
-	return platform_driver_register(&mt7621_pci_driver);
-}
-
-module_init(mt7621_pci_init);
+builtin_platform_driver(mt7621_pci_driver);