tg3: Use pci_read_vpd() instead of private method

If the driver needs to use PCI configuration space to read the VPD data,
the accesses could collide with the pci_read_vpd() function.  This patch
converts the driver to use pci_read_vpd() to avoid any potential
collisions.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>