[PowerPC][Book-E] Fix missing load base in elf_cpu_parse_dynamic().

When I implemented MD DYNAMIC parsing, I was originally passing a
linker_file_t so that the MD code could relocate pointers.

However, it turns out this isn't even filled in until later, so it was
always 0.

Just pass the load base (ef->address) directly, as that's really the only
thing we were interested in in the first place.

This fixes a crash on RB800 where it was trying to write to an unmapped
address when updating the GOT.

Reviewed by: jhibbits
Sponsored by: Tag1 Consulting, Inc.
Differential Revision: https://reviews.freebsd.org/D24105