smsc95xx: fix register dump of last register

This patch fixes the ethtool register dump for smsc95xx to dump
all 4 bytes of the final register (COE_CR) instead of just the
first byte.

Signed-off-by: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: David S. Miller <davem@davemloft.net>