net/wan: use module_pci_driver

This patch converts the drivers in drivers/net/wan/* to use
module_pci_driver() macro which makes the code smaller and a bit simpler.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Francois Romieu <romieu@fr.zoreil.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>