davinci_emac: off by one

This off by one error was found by smatch.

drivers/net/davinci_emac.c +2390 emac_dev_open(13) error: buffer overflow 'priv->mac_addr' 6 <= 6

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>