perf/core: Call perf_prepare_sample() before running BPF

As BPF can access sample data, it needs to populate the data.  Also
remove the logic to get the callchain specifically as it's covered by
the perf_prepare_sample() now.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230118060559.615653-9-namhyung@kernel.org