cxgb4: remove unused vpd_cap_addr

It is likely that this is a leftover from T3 driver heritage. cxgb4 uses
the PCI core VPD access code that handles detection of VPD capabilities.

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>