perf bench mem: The -o and -n options are mutually exclusive

perf bench mem: The -o and -n options are mutually exclusive

 -o, --only-prefault   Show only the result with page faults before mem*
 -n, --no-prefault     Show only the result without page faults before mem*

Makes no sense to call together. Applies to both memset and memcpy.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1402942467-10671-8-git-send-email-davidlohr@hp.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>