serial: txx9: add missing platform_driver_unregister() on error in serial_txx9_init

Add the missing platform_driver_unregister() before return
from serial_txx9_init in the error handling case when failed
to register serial_txx9_pci_driver with macro ENABLE_SERIAL_TXX9_PCI
defined.

Fixes: ab4382d2 ("tty: move drivers/serial/ to drivers/tty/serial/")
Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
Link: https://lore.kernel.org/r/20201103084942.109076-1-miaoqinglang@huawei.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_txx9.c

@@ -1280,6 +1280,9 @@ static int __init serial_txx9_init(void)
 
 #ifdef ENABLE_SERIAL_TXX9_PCI
 	ret = pci_register_driver(&serial_txx9_pci_driver);
+	if (ret) {
+		platform_driver_unregister(&serial_txx9_plat_driver);
+	}
 #endif
 	if (ret == 0)
 		goto out;