[PATCH v3] ieee1275: Fix crash in of_path_of_nvme when of_path is empty

[John Paul Adrian Glaubitz]

Hi!

As suggested by James Clarke earlier on this mailing list today, I
have modified of_path_of_nvme such that it behaves the same way as
of_path_of_scsi and just returns NULL when the call to find_obppath
returns NULL.

This makes much more sense than what my previous patch did as we
don't want of_path_of_nvme to return anything but NULL when not
run on a system not based on Open Firmware.

Thanks,
Adrian