perf annotate: Loop group events directly in annotation__calc_percent()

perf annotate: Loop group events directly in annotation__calc_percent()

We need to bring in 'struct hists' object and for that we need 'struct
perf_evsel' object in the scope.

Switching the group data loop with the evsel group loop.  It does the
same thing, but it brings evsel object, that we can use later get the
'struct hists' object.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20180804130521.11408-8-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>