perf sched latency: Fix subcommand matching error

perf sched latency use strncmp to match subcommands which matching does not
meet expectation.

Before:

  # perf sched lat1234 >/dev/null
  # echo $?
  0
  #

Solution: Use strstarts to match subcommand.

After:

   # perf sched lat1234

   Usage: perf sched [<options>] {record|latency|map|replay|script|timehist}

      -D, --dump-raw-trace  dump raw trace in ASCII
      -f, --force           don't complain, do it
      -i, --input <file>    input file name
      -v, --verbose         be more verbose (show symbol address, etc)

  # echo $?
  129
  #
  # perf sched lat >/dev/null
  # echo $?
  0
  #

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220808092408.107399-3-yangjihong1@huawei.com


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