PCI: Be a bit defensive in quirk_nvidia_ck804() so we don't risk dereferencing a...

pci_get_slot() may return NULL if nothing was found.  quirk_nvidia_ck804()
does not check the value returned from pci_get_slot(), so it may end up
causing a NULL pointer deref.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>