Marvell Neta's transmit descriptor (txdesc) is allocated by dma_alloc_coherent()
but not zeroed before calling mvneta_send the first time. This can cause spurious
transmit errors due to improperly set bits in txdesc's cmd_sts field.

Fix initial transmit errors by always writing whole cmd_sts field instead of ORing
the bits.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>