[PATCH] libertas: call SET_NETDEV_DEV from common code

Move usage of SET_NETDEV_DEV into common code since it has nothing
to do with bus-specific devices.  Also fixes a bug where the mesh
device was getting SET_NETDEV_DEV called after register_netdevice,
resulting in no 'device' link in /sys/class/net/mshX/.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>