perf test: Replace 'grep | wc -l' with 'grep -c'

To count the number of results from grep, use the '-c' parameter
instead of piping it to 'wc'.

See also https://www.shellcheck.net/wiki/SC2126



Signed-off-by: Diederik de Haas <didi.debian@cknow.org>
Acked-by: Carsten Haitzler <carsten.haitzler@arm.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: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230201214945.127474-2-didi.debian@cknow.org


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