ide: ide_scan_pcibus(): check __pci_register_driver return value

drivers/ide/setup-pci.c: In function 'ide_scan_pcibus':
drivers/ide/setup-pci.c:879: warning: ignoring return value of '__pci_register_driver', declared with attribute warn_unused_result

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>