perf evlist: Fix missing event name init for default event

When no event is given to perf record, perf top, a default event is
initialized (cycles). However, perf_evlist__add_default() was not
setting the symbolic name for the event. Perf top worked simply because
it was reconstructing the name from the event code. But it should not
have to do this. This patch initializes the evsel->name field properly.

This second version improves the code flow on the non error path.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20110607161936.GA8163@quad
Signed-off-by: Stephane Eranian <eranian@google.com>
[committer note: Use perf_evsel__delete() instead of plain free()]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>