Don't read DSN on VFs that do not have the PCI capability.

Fixes: 03213a99 ("bnxt: move bp->switch_id initialization to PF probe")
Signed-off-by: NVasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: NMichael Chan <michael.chan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>