pci_driver.probe should return a meaningful errno, not -1.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>