PCI: fix up error messages for pci_bus registering

Due to the class_device cleanup of pci_bus, the error messages when
things go wrong are incorrect.  So fix this up to properly report what
is really happening, if things go wrong.

Thanks to Kay for pointing out the issue.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>