libbpf: Use correct return pointer in attach_raw_tp

We need to pass '*link' to final libbpf_get_error,
because that one holds the return value, not 'link'.

Fixes: 4fa5bcfe

 ("libbpf: Allow BPF program auto-attach handlers to bail out")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221114145257.882322-1-jolsa@kernel.org