Check for a 'pci' prefix rather than a full match in get_addr_props

[jhibbits]

Summary

Newer OPAL device trees, such as those on POWER9 systems, use 'pciex' for
device_type, not 'pci'. Rather than enumerating all possible variants, just
check for a 'pci' prefix.

[nwhitehorn]

It's mildly stupid, since the universe of pci* isn't big, but I think I would prefer a check for "pci" || "pciex" to just checking the first three characters.

[jhibbits]

Change to nwhitehorn's preference. Either is fine with me.

[nwhitehorn]

Don't you want strcmp() == 0?

[jhibbits]

I should probably caffeinate before making such trivial changes.