b44: call netif_napi_del()

When the driver gets unregistered a call to netif_napi_del() was
missing, this all was also missing in the error paths of
b44_init_one().

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>