powerpc/pci: Remove redundant pcnet32 fixup

The pcnet32 driver has had in its device id table for some time a match
against the "broken" vendor ID.  No need to fake out the vendor ID
with an explicit fixup.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>