Revert "serial: max310x: pass return value of spi_register_driver"

This reverts commit 51f689cc.

Because of recent interactions with developers from @umn.edu, all
commits from them have been recently re-reviewed to ensure if they were
correct or not.

Upon review, this commit was found to be incorrect for the reasons
below, so it must be reverted.  It will be fixed up "correctly" in a
later kernel change.

This change did not properly unwind from the error condition, so it was
not correct.

Cc: Kangjie Lu <kjlu@umn.edu>
Acked-by: NJiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20210503115736.2104747-11-gregkh@linuxfoundation.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -1518,10 +1518,10 @@ static int __init max310x_uart_init(void)
 		return ret;
 
 #ifdef CONFIG_SPI_MASTER
-	ret = spi_register_driver(&max310x_spi_driver);
+	spi_register_driver(&max310x_spi_driver);
 #endif
 
-	return ret;
+	return 0;
 }
 module_init(max310x_uart_init);