cxgb3 - Fix dev->priv usage

cxgb3 used netdev_priv() and dev->priv for different purposes.
In 2.6.23, netdev_priv() == dev->priv, cxgb3 needs a fix.
This patch is a partial backport of Dave Miller's changes in the
net-2.6.24 git branch.

Without this fix, cxgb3 crashes on 2.6.23.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>