Use pci_vpd_alloc() to dynamically allocate a properly sized buffer and
read the full VPD data into it.

This simplifies the code, and we no longer have to make assumptions about
VPD size.

Link: https://lore.kernel.org/r/62522a24-f39a-2b35-1577-1fbb41695bed@gmail.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>