serial: max310x: pass return value of spi_register_driver

spi_register_driver() may fail, so let's pass its return value upstream.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -1467,10 +1467,10 @@ static int __init max310x_uart_init(void)
 		return ret;
 
 #ifdef CONFIG_SPI_MASTER
-	spi_register_driver(&max310x_spi_driver);
+	ret = spi_register_driver(&max310x_spi_driver);
 #endif
 
-	return 0;
+	return ret;
 }
 module_init(max310x_uart_init);