net: stmmac: improve .set_clk_tx_rate() method error message

Improve the .set_clk_tx_rate() method error message to include the
PHY interface mode along with the speed, which will be helpful to
the RK implementations.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/E1uPjjx-0049r5-NN@rmk-PC.armlinux.org.uk


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