sh_eth: stop reading ECMR in sh_eth_dev_init()

The code in sh_eth_dev_init()  twiddling the ECMR bits always looked a bit
strange to me:  if one intends to respect 'mdp->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>