Use numbered adapter registration to always have the same hardware bus
show up at the same number.

PWRficient 1682M has three buses, they are all on the same PCI device but
different functions. So do the simple thing and register them based on
function number. Future products, if having a different number of busses,
are expected to have similar behaviour w.r.t. device/function layout.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>