net: stmmac: dwmac-qcom-ethqos: Update link clock rate only for RGMII

Updating link clock rate for different speeds is only needed when
using RGMII, as that mode requires changing clock speed when the link
speed changes. Let's restrict updating the link clock speed in
ethqos_update_link_clk() to just RGMII. Other modes such as SGMII
only need to enable the link clock (which is already done in probe).

Signed-off-by: Sarosh Hasan <quic_sarohasa@quicinc.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Tested-by: Andrew Halaney <ahalaney@redhat.com> # sa8775p-ride
Reviewed-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>