ARM: dts: keystone: fix the clock node for mdio

Currently the MDIO clock is pointing to clkpa instead of clkcpgmac.
MDIO is part of the ethss and the clock should be clkcpgmac.
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>

arch/arm/boot/dts/keystone.dtsi

@@ -273,7 +273,7 @@ mdio: mdio@02090300 {
 			#size-cells = <0>;
 			reg		= <0x02090300 0x100>;
 			status = "disabled";
-			clocks = <&clkpa>;
+			clocks = <&clkcpgmac>;
 			clock-names = "fck";
 			bus_freq	= <2500000>;
 		};