net: sun8i_emac: Don't hand out TX descriptor too early

net: sun8i_emac: Don't hand out TX descriptor too early

When initialising the TX DMA descriptors, we mostly chain them up,
but of course don't know about any data or its length yet.
That means they are still invalid, and the OWN bit should NOT be set
yet.

In fact when we later tell the MAC about the beginning of the chain,
and enable TX DMA in the start() routine, the MAC will start fetching
TX descriptors prematurely, as it can be seen by dumping the TX_DMA_STA
and TX_DMA_CUR_DESC registers.

Clear the owner bit, to not give the MAC the wrong illusion that it
owns the descriptors already.

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>