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

drivers/net/mv643xx_eth.c

@@ -2247,7 +2247,7 @@ static void port_start(struct mv643xx_eth_private *mp)
 	 * frames to RX queue #0, and include the pseudo-header when
 	 * calculating receive checksums.
 	 */
-	mv643xx_eth_set_features(dev, dev->features);
+	mv643xx_eth_set_features(mp->dev, mp->dev->features);
 
 	/*
 	 * Treat BPDUs as normal multicasts, and disable partition mode.