perf evsel: Update function names in debug messages

perf_event_open() was renamed to sys_perf_event_open(); update the debug
messages to reflect this.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1395169842-1399-1-git-send-email-artagnon@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>