serial: max310x: add comments for membase address workaround

Add comments about workaround used to configure membase address. This
follows suggestions made during review of a sc16is7xx driver patch to
add the same workaround.

Link: https://lore.kernel.org/lkml/2936e18f-44ea-faed-9fa0-2ddefe7c3194@linux.intel.com
Link: https://lore.kernel.org/lkml/20230801131655.80bd8f97f018dda6155d65f6@hugovil.com/
Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20230803140551.970141-1-hugo@hugovil.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -1369,6 +1369,11 @@ static int max310x_probe(struct device *dev, const struct max310x_devtype *devty
 		s->p[i].port.flags	= UPF_FIXED_TYPE | UPF_LOW_LATENCY;
 		s->p[i].port.iotype	= UPIO_PORT;
 		s->p[i].port.iobase	= i;
+		/*
+		 * Use all ones as membase to make sure uart_configure_port() in
+		 * serial_core.c does not abort for SPI/I2C devices where the
+		 * membase address is not applicable.
+		 */
 		s->p[i].port.membase	= (void __iomem *)~0;
 		s->p[i].port.uartclk	= uartclk;
 		s->p[i].port.rs485_config = max310x_rs485_config;