net: sun8i_emac: Drop unneeded cache invalidation before sending

There is no reason to invalidate a TX descriptor before we are setting
it up, as we will only write to a field.

Remove the not needed invalidate_dcache_range() call.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Amit Singh Tomar <amittomer25@gmail.com> # Pine64+
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>