perf tests mmap: Show which tracepoint is failing

perf tests mmap: Show which tracepoint is failing

In the 'perf test "mmap interface"' we try creating events for several
tracepoints, but when perf_evsel__new() fails we're not showing which
one is failing, fix that to help diagnosing problems, such as the
syscall tracepoints ones being found and fixes in this merge window.

Now the failing tests shows:

  # perf test -v "mmap interface"
 4: Read samples using the mmap interface                 :
  --- start ---
  test child forked, pid 14311
  <SNIP>
  perf_evsel__new(sys_enter_getppid)
  test child finished with -1
  ---- end ----
  Read samples using the mmap interface: FAILED!
  #

Now to check why the syscalls:sys_enter_getppid is failing...

  # ls -la /sys/kernel/debug/tracing/events/syscalls/sys_enter_getppid
  ls: cannot access '/sys/kernel/debug/tracing/events/syscalls/sys_enter_getppid': No such file or directory
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-44xk0ycdzrfzx1o9rklf5itl@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>