perf/trace/scripting: syscall-counts-by-pid script cleanup

A small fix for the syscall counts by pid script:

- silence the match output in the shell script

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1273466820-9330-9-git-send-email-tzanussi@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>