fmvj18x_cs: fix incorrect indexing of dev->dev_addr[] when copying the MAC address

fix incorrect indexing of dev->dev_addr[] when copying the MAC address
of FMV-J182 at buf[5].

Signed-off-by: Ken Kawasaki <ken_kawasaki@nifty.com>
Signed-off-by: David S. Miller <davem@davemloft.net>