serial: port: Assign ->iotype correctly when ->iobase is set

Currently the ->iotype is always assigned to the UPIO_MEM when
the respective property is not found. However, this will not
support the cases when user wants to have UPIO_PORT to be set
or preserved.  Support this scenario by checking ->iobase value
and default the ->iotype respectively.

Fixes: 1117a6f ("serial: 8250_of: Switch to use uart_read_port_properties()")
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/20250124161530.398361-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: andy-shev

drivers/tty/serial/serial_port.c

@@ -173,6 +173,7 @@ EXPORT_SYMBOL(uart_remove_one_port);
  * The caller is responsible to initialize the following fields of the @port
  *   ->dev (must be valid)
  *   ->flags
+ *   ->iobase
  *   ->mapbase
  *   ->mapsize
  *   ->regshift (if @use_defaults is false)
@@ -214,7 +215,7 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 	/* Read the registers I/O access type (default: MMIO 8-bit) */
 	ret = device_property_read_u32(dev, "reg-io-width", &value);
 	if (ret) {
-		port->iotype = UPIO_MEM;
+		port->iotype = port->iobase ? UPIO_PORT : UPIO_MEM;
 	} else {
 		switch (value) {
 		case 1: