serial: max310x: unregister uart driver in case of failure and abort

The macro "spi_register_driver" invokes the function
"__spi_register_driver()" which has a return type of int and can fail,
returning a negative value in such a case. This is currently ignored and
the init() function yields success even if the spi driver failed to
register.

Fix this by collecting the return value of "__spi_register_driver()" and
also unregister the uart driver in case of failure.

Cc: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Atul Gopinathan <atulgopinathan@gmail.com>
Link: https://lore.kernel.org/r/20210503115736.2104747-12-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -1518,10 +1518,12 @@ 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);
+	if (ret)
+		uart_unregister_driver(&max310x_uart);
 #endif
 
-	return 0;
+	return ret;
 }
 module_init(max310x_uart_init);