discovery: fix stack offset write back in stage 5

The handling of multiple stack offsets introduced a bug in the
dispaying and writing back in the single object single stack
offset adaption in postproc_stage5(). We are writing back the
memory address of our stack_offs[] array. So use stack_offs[0]
instead.

For now we don't support adation of more than a single stack
offset but that support will follow.
ugtrain: add support for multi stack offset adaption

This mainly affects discovery stage 5. In case that not all cases
of target memory object allocation have been triggered, we consider
the whole adaption for that memory object as failed. In other words:
We don't write back incompletely adapted stack offsets.
discovery: fail stage 5 if too many stack offsets

If we discover more than the configured number of stack offsets,
then we can't really decide which ones are correct. There might
be object allocation cases the user didn't think of, yet.