net: phy: micrel: allow usage of generic ethernet-phy clock

The generic ethernet-phy binding allows describing an external clock since
commit 350b7a258f ("dt-bindings: net: phy: Document support for external PHY clk")
for cases where the phy is not supplied by an oscillator but instead
by a clock from the host system.

And the old named "rmii-ref" clock from 2014 is only specified for phys
of the KSZ8021, KSZ8031, KSZ8081, KSZ8091 types.

So allow retrieving and enabling the optional generic clock on phys that
do not provide a rmii-ref clock.

Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20231201150131.326766-3-heiko@sntech.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/micrel.c

@@ -2021,6 +2021,11 @@ static int kszphy_probe(struct phy_device *phydev)
 				   rate);
 			return -EINVAL;
 		}
+	} else if (!clk) {
+		/* unnamed clock from the generic ethernet-phy binding */
+		clk = devm_clk_get_optional_enabled(&phydev->mdio.dev, NULL);
+		if (IS_ERR(clk))
+			return PTR_ERR(clk);
 	}
 
 	if (ksz8041_fiber_mode(phydev))