perf build-id: Ensure struct build_id is empty before use

perf build-id: Ensure struct build_id is empty before use

If a build ID is read then not all code paths may ensure it is empty
before use. Initialize the build_id to be zero-ed unless there is
clear initialization such as a call to build_id__init.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250724163302.596743-6-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>