drivers: net: xilinx_emaclite: Add missing parameter kerneldoc

The txqueue parameter to the watchdog callback is unused in this
driver. But it still needs to be documented.

Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>