cxgb4: Validate VPD checksum with pci_vpd_check_csum()

Validate the VPD checksum with pci_vpd_check_csum() to simplify the code.

Link: https://lore.kernel.org/r/70404ece-0036-c0ce-f824-f5637e54115e@gmail.com


Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>