ppc: Fix endianness bug which caused node_add_child to fail.

Code used:

  le32toh (reg_field + 0x1000)

instead of the correct version:

  le32toh (reg_field) + 0x1000

The first incorrect form adds 0x1000 to the possibly byte-swapped
registry field, corrupting it.

I used the following command to look for problems in the remaining
code but did not find any:

  git grep -P 'le\d+toh\s*\([^)]*\+'

NOTE that 'htole32 (reg_field - 0x1000)' is correct.