Currently pipe mode doesn't set the file size and it results in a
misleading message of 0 data size at the end.  Although it might miss
some accounting for pipe header or more, just displaying the data size
would reduce the possible confusion.

Before:
  $ perf record -o- perf test -w noploop | perf report -i- -q --percent-limit=1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.000 MB - ]    <======  (here)
      99.58%  perf     perf                  [.] noploop

After:
  $ perf record -o- perf test -w noploop | perf report -i- -q --percent-limit=1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.229 MB - ]
      99.46%  perf     perf                  [.] noploop
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20240112231340.779469-1-namhyung@kernel.org