perf tools: Don't access evsel->name directly

perf tools: Don't access evsel->name directly

One needs to use perf_evsel__name() so that if needed the name gets
synthesized and stored in evsel->name, from where perf_evsel__name()
will serve from them on.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-ml7zbenjmri9bghmrea0jm0d@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>