arm64: dts: ti: k3-j7200: Fix MDIO clock

cpsw5g_mdio clock is incorrect. Fix it.

Fixes: 008a8d71

 ("arm64: dts: ti: k3-j7200: Add CPSW5G nodes")
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>