perf evlist: Fix the class prefix for 'struct evlist' branch_type methods

To differentiate from libperf's 'struct perf_evlist' methods.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>