perf tests: Remove bash constructs from stat_all_pmu.sh

The tests were passing but without testing and were printing the
following:

  $ ./perf test -v 90
  90: perf all PMU test                                               :
  --- start ---
  test child forked, pid 51650
  Testing cpu/branch-instructions/
  ./tests/shell/stat_all_pmu.sh: 10: [:
   Performance counter stats for 'true':

             137,307      cpu/branch-instructions/

         0.001686672 seconds time elapsed

         0.001376000 seconds user
         0.000000000 seconds sys: unexpected operator

Changing the regexes to a grep works in sh and prints this:

  $ ./perf test -v 90
  90: perf all PMU test                                               :
  --- start ---
  test child forked, pid 60186
  [...]
  Testing tlb_flush.stlb_any
  test child finished with 0
  ---- end ----
  perf all PMU test: Ok

Signed-off-by: James Clark <james.clark@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20211028134828.65774-4-james.clark@arm.com


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