bnx2x: Obtain Bus Device Function from register

BDF was obtained from kernel but since in virtualized environment
(e.g. physical device assigment in KVM) the function number may
not be the real one, the info must be obtained from the device.

Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>