perf tests: No need to set attr.sample_freq in the perf time to TSC test

We were asking for a 4kHz sample_freq, making the test fail needlessly
when the system reduced /proc/sys/kernel/perf_event_max_sample_rate
below that.

In this test we only look at the PERF_SAMPLE_TIME fields in PERF_RECORD_
meta events, no need to set sample_freq.

Thanks to Namhyung for suggesting that max_sample_rate could be the
reason for the test failure, seeing the 'perf test -vv' output I sent.

Before:

  # echo 1000 > /proc/sys/kernel/perf_event_max_sample_rate
  # perf test TSC
  45: Test converting perf time to TSC   : FAILED!

After:

  # perf test TSC
  45: Test converting perf time to TSC   : Ok
  # cat /proc/sys/kernel/perf_event_max_sample_rate
  1000

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-lcob05qhawkuvsyuu9g1fld5@git.kernel.org


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