With perf inject -b, it synthesizes build-id event for DSOs.  But it
missed to set the size and resulted in having trailing zeros.

As perf record sets the size in write_build_id(), let's set the size
here as well.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221119002750.1568027-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>