net: stmmac: intel: use generic stmmac_set_clk_tx_rate()

Use the generic stmmac_set_clk_tx_rate() to configure the MAC transmit
clock.

Note that given the current unpatched driver structure,
plat_dat->fix_mac_speed will always be populated with
kmb_eth_fix_mac_speed(), even when no clock is present. We preserve
this behaviour in this patch by always initialising plat_dat->clk_tx_i
and plat_dat->set_clk_tx_rate.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1tna0f-0052sw-8r@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>