MAINTAINERS: record lib/buildid.c as owned by BPF subsystem

MAINTAINERS: record lib/buildid.c as owned by BPF subsystem

Build ID fetching code originated from ([0]), and is still both owned
and heavily relied upon by BPF subsystem.

Fix the original omission in [0] to record this fact in MAINTAINERS.

  [0] bd7525dacd7e ("bpf: Move stack_map_get_build_id into lib")

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20240909190426.2229940-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>