net: dsa: microchip: fix RGMII error in KSZ DSA driver

[ Upstream commit 278d65cc ]

The driver should return RMII interface when XMII is running in RMII mode.

Fixes: 0ab7f6bf

 ("net: dsa: microchip: ksz9477: use common xmii function")
Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Acked-by: Jerry Ray <jerry.ray@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/1716932066-3342-1-git-send-email-Tristram.Ha@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>