perf thread-stack: Tidy thread_stack__no_call_return() by adding more local variables

Make thread_stack__no_call_return() more readable by adding more local
variables.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20190109091835.5570-4-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>