Options marked OPTION_UINTEGER or OPTION_U64 clearly indicates that an
unsigned value is expected, so just error out when a negative value is
passed, instead of returning something undesired to the tool.

E.g.:

  # perf bench futex hash -t -4
  # Running 'futex/hash' benchmark:
   Error: switch `t' expects an unsigned numerical value
   Usage: perf bench futex hash <options>

      -t, --threads <n>     Specify amount of threads
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-2mdn8s2raatyhz7tamrsz22r@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>