perf trace: Do not accept --no-syscalls together with -e

Doesn't make sense and was causing a segfault, fix it.

  # trace -e clone --no-syscalls --event sched:*exec firefox
  The -e option can't be used with --no-syscalls.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ccrahezikdk2uebptzr1eyyi@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>