libbpf: checkpatch: Fixed code alignments in btf.c

Fixed some checkpatch issues in btf.c

Signed-off-by: Kang Minchul <tegongkang@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20221113190648.38556-2-tegongkang@gmail.com