perf report: Fix stdio event name header printing

perf report: Fix stdio event name header printing

In the past we tried to avoid printing the name of the event when just
one event was found in the perf.data file, after some refactorings it
ended up not printing the event name if just one hist_entry was found in
one of the events.

Fix it by always printing the name of the event, even if just one is
found.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-kikr0c7ou55bd9caok8569rf@git.kernel.org
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>