perf list: Fix --raw-dump argument

While adding usage information, 44d742e (perf list: Add usage,
2013-10-30) broke

  $ perf list --raw-dump

Fix this by making raw-dump a proper argument.

Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>