[PowerPC] [BookE] Fix read past end of struct

[bdragon]

Summary

This was causing panics for me when using GCC 6.4.

Replace overly clever code that was reading past the end of a struct with a basic double loop.

[jhibbits]

Looks good for what we can do for now. I really should clean up the whole DPAA interface bits, so we don't need to do that loop. But since it's only executed on bootup, it's not a very high priority task.