ravb: stop reading ECMR in ravb_emac_init()

The code in ravb_emac_init() twiddling the ECMR bits always looked a bit
strange to me: if one intends to respect 'priv->duplex', why save old value
of the ECMR.DM bit?   As all the other bits are zeroed anyway, we don't
really need to read ECMR before writing to it.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>