perf script: Use event_format__fprintf()

Another case where we a1a58707 ("perf script: Use fprintf like
printing uniformly") forgot to redirect output to the FILE descriptor,
fix this too.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: yuzhoujian <yuzhoujian@didichuxing.com>
Link: http://lkml.kernel.org/n/tip-jmwx4pgfezw98ezfoj9t957s@git.kernel.org


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