perf trace: The return from 'write' isn't a pid

When adding a explicit beautifier for the 'write' syscall when the BPF
based buffer collector was introduced there was a cut'n'paste error that
carried the syscall_fmt->errpid setting from a nearby syscall (waitid)
that returns a pid.

So the write return was being suppressed by the return pretty printer,
remove that field, reverting it back to the default return handler, that
prints positive numbers as-is and interpret negative values as errnos.

I actually introduced the problem while making Howard's original patch
work just with the 'write' syscall, as we couldn't just look for any
buffers, the ones that are filled in by the kernel couldn't use the same
sys_enter BPF collector.

Fixes: b257fac12f38d7f5 ("perf trace: Pretty print buffer data")
Reported-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/lkml/bcf50648-3c7e-4513-8717-0d14492c53b9@linaro.org
Link: https://lore.kernel.org/all/Zt8jTfzDYgBPvFCd@x1/#t
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>