[AMDGPU][SplitModule] Keep looking for more dependencies after finding an indirect call (#93480)

This is just something I noticed while going over this pass logic one
more time and didn't cause issues (yet). If we find an indirect call, we
stop looking assuming we added all functions to the list, but if not all
functions in the module were indirectly callable, some may still be
missing.

Just to be safe, keep looking until we did everything we could to find
dependencies, so we don't accidentally miss one.