nvidiafb/rivafb: switch to pci_get refcounting

Switch to pci_get refcounting APIs

[adaplas]
Fix a long-standing bug where the return value of
pci_find_slot()/pci_get_bus_and_slot() is ignored.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>