serial: port: Always update ->iotype in __uart_read_properties()

The documentation of the __uart_read_properties() states that
->iotype member is always altered after the function call, but
the code doesn't do that in the case when use_defaults == false
and the value of reg-io-width is unsupported. Make sure the code
follows the documentation.

Note, the current users of the uart_read_and_validate_port_properties()
will fail and the change doesn't affect their behaviour, neither
users of uart_read_port_properties() will be affected since the
alteration happens there even in the current code flow.

Fixes: e894b60 ("serial: port: Introduce a common helper to read properties")
Cc: stable <stable@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250124161530.398361-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_port.c

@@ -228,11 +228,11 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 			port->iotype = device_is_big_endian(dev) ? UPIO_MEM32BE : UPIO_MEM32;
 			break;
 		default:
+			port->iotype = UPIO_UNKNOWN;
 			if (!use_defaults) {
 				dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
 				return -EINVAL;
 			}
-			port->iotype = UPIO_UNKNOWN;
 			break;
 		}
 	}