net: stmmac: Fix CSR divider comment

net: stmmac: Fix CSR divider comment

The comment in declaration of STMMAC_CSR_250_300M
incorrectly describes the constant as '/* MDC = clk_scr_i/122 */'
but the DWC Ether QOS Handbook version 5.20a says it is
CSR clock/124.

Signed-off-by: Jan Petrous (OSS) <jan.petrous@oss.nxp.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20241205-upstream_s32cc_gmac-v8-1-ec1d180df815@oss.nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>