mv643xx_eth: report netdev name in all printks

In error and warning printks, always report the netdevice name
instead of the port index (the latter has no meaning when there
are multiple mv643xx_eth silicon blocks in the system.)

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Reviewed-by: Tzachi Perelstein <tzachi@marvell.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>