MAINTAINERS: Add scripts/pahole-flags.sh to BPF section

Currently, scripts/pahole-flags.sh has no formal maintainer. Add it to
the BPF section so that patches to it can be properly reviewed and
picked up.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220201205624.652313-2-nathan@kernel.org