[InstrProfiling] Support relative CountersPtr for PlatformOther

D104556 change the CountersPtr to be relative, however, it did not
update the pointer initialization in  __llvm_profile_register_function,
so the platform (eg:AIX) that use __llvm_profile_register_function is now totaly
broken, any PGO code will SEGV.

This patch update the code to reflect that the Data->CountersPtr is now
relative.

Reviewed By: MaskRay, davidxl

Differential Revision: https://reviews.llvm.org/D108304