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: 1117a6fdc7c1 ("serial: 8250_of: Switch to use uart_read_port_properties()")
Fixes: e894b6005dce ("serial: port: Introduce a common helper to read properties")
Cc: stable <[e-mail]>
Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/serial_port.c

···
  * 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)
···
 	/* 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: