mv643xx_eth: Fix build regression.

From Stephen Rothwell:

--------------------
After merging the final tree, today's linux-next build (powerpc chrp32_defconfig)
failed like this:

drivers/net/mv643xx_eth.c: In function 'port_start':
drivers/net/mv643xx_eth.c:2250: error: 'dev' undeclared (first use in this function)

Caused by commit aad59c43 ("net: mv643xx: convert to hw_features").
--------------------

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>