net: dsa: microchip: Fix probing KSZ87xx switch with DT node for host port

The ksz8795 and ksz9477 drivers differ in the way they count ports.
For ksz8795, ksz_device::port_cnt does not include the host port
whereas for ksz9477 it does.  This inconsistency was fixed in Linux
5.11 by a series of changes, but remains in 5.10-stable.

When probing, the common code treats a port device node with an
address >= dev->port_cnt as a fatal error.  As a minimal fix, change
it to compare again dev->mib_port_cnt.  This is the length of the
dev->ports array that the port number will be used to index, and
always includes the host port.

Cc: Woojung Huh <woojung.huh@microchip.com>
Cc: Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
Cc: Michael Grzeschik <m.grzeschik@pengutronix.de>
Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Ben Hutchings <ben.hutchings@mind.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: bwh-mind

drivers/net/dsa/microchip/ksz_common.c

@@ -432,7 +432,7 @@ int ksz_switch_register(struct ksz_device *dev,
 				if (of_property_read_u32(port, "reg",
 							 &port_num))
 					continue;
-				if (port_num >= dev->port_cnt)
+				if (port_num >= dev->mib_port_cnt)
 					return -EINVAL;
 				of_get_phy_mode(port,
 						&dev->ports[port_num].interface);