linux-wandboard

spidernet: invalidate unused pointer.

Invalidate a pointer as its pci_unmap'ed; this is a bit of
paranoia to make sure hardware doesn't continue trying to
DMA to it.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>