libbpf: fix formatting of bpf_object__append_subprog_code

libbpf: fix formatting of bpf_object__append_subprog_code

The commit 6c918709bd30 ("libbpf: Refactor bpf_object__reloc_code")
added the bpf_object__append_subprog_code() with incorrect indentations.
Use tabs instead. (This also makes a consequent commit better readable.)

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20251019202145.3944697-14-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>