serial: 8250: 8250_core: Fix missing unlock on error in serial8250_register_8250_port()

Add the missing unlock before return from function serial8250_register_8250_port()
in the error handling case.

Signed-off-by: Wei Yongjun <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/8250/8250_core.c

···
 		if (!has_acpi_companion(uart->port.dev)) {
 			gpios = mctrl_gpio_init(&uart->port, 0);
 			if (IS_ERR(gpios)) {
-				if (PTR_ERR(gpios) != -ENOSYS)
-					return PTR_ERR(gpios);
+				if (PTR_ERR(gpios) != -ENOSYS) {
+					ret = PTR_ERR(gpios);
+					goto out_unlock;
+				}
 			} else {
 				uart->gpios = gpios;
 			}
···
 		}
 	}
 
+out_unlock:
 	mutex_unlock(&serial_mutex);
 
 	return ret;