net: fec_mxc: Fix clk_ref rate on iMX93

net: fec_mxc: Fix clk_ref rate on iMX93

i.MX93 FEC ENET port supports two mode: RGMII and RMII. For RGMII,
there is an internal /2 divider, so the freq needs to set with (*2),
otherwise the speed will not reach 1G and cause communication error
in some network environments. For RMII, the clk path is
ccm -> enet tx_clk pin -> pad loop back to enet, no /2 divider.

So fix for RGMII mode with freq multiplied by 2.

Fixes: 09de565f76b ("net: fec_mxc: support i.MX93")
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>