Compiling this module gave a warning that the return value of
'pci_bus_add_device()' was not checked.

This patch adds that check and an output message
Signed-off-by: Douglas Thompson <dougthompson@xmission.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>