perf auxtrace: Add missing 'struct perf_sample' forward declaration

Its needed, was being obtained indirectly, fix it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-c3k1il7sm28old4e22nwlm7l@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/auxtrace.h

@@ -24,6 +24,7 @@ struct perf_session;
 struct evlist;
 struct perf_tool;
 struct perf_mmap;
+struct perf_sample;
 struct option;
 struct record_opts;
 struct perf_record_auxtrace_info;