DM9000: fix use of kfree() on net device

The DM9000 network driver is calling kfree() on an netdev
causing the system to oops if the probe fails. The right
thing to do is call free_netdev().

Thanks to Russell King for spotting this.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>