perf callchain lbr: Make the leaf IP that of the sample

The current IP of a leaf function when reported from a perf record with
"--call-graph lbr" is the "to" field of the LBR branch stack record.

The sample for the event being recorded may be further into the function
and there may be inlining information associated with it.

Rather than use the branch stack "to" field in this case switch to the
callchain appending the sample->ip and thereby allowing the inline
information to show.

Before this change:
```
$ perf record --call-graph lbr perf test -w inlineloop
...
$ perf script --fields +srcline
...
perf-inlineloop 467586 4649.344493: 950905 cpu_core/cycles/P:
55dfda2829c0 parent+0x0 (perf)
inlineloop.c:31
55dfda282a96 inlineloop+0x86 (perf)
inlineloop.c:47
55dfda236420 run_workload+0x59 (perf)
builtin-test.c:715
55dfda236b03 cmd_test+0x413 (perf)
builtin-test.c:825
...
```

After this change:
```
$ perf record --call-graph lbr perf test -w inlineloop
...
$ perf script --fields +srcline
...
perf-inlineloop 529703 11878.680815: 950905 cpu_core/cycles/P:
555ce86be9e6 leaf+0x26
inlineloop.c:20 (inlined)
555ce86be9e6 middle+0x26
inlineloop.c:27 (inlined)
555ce86be9e6 parent+0x26 (perf)
inlineloop.c:32
555ce86bea96 inlineloop+0x86 (perf)
inlineloop.c:47
555ce8672420 run_workload+0x59 (perf)
builtin-test.c:715
555ce8672b03 cmd_test+0x413 (perf)
builtin-test.c:825
...
```

Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Krzysztof Łopatowski <krzysztof.m.lopatowski@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Weilin Wang <weilin.wang@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>