libbpf: Use direct error codes for kprobe/uprobe attach

libbpf: Use direct error codes for kprobe/uprobe attach

perf_event_open_probe() and perf_event_{k,u}probe_open_legacy() helpers
are returning negative error codes directly on failure. This commit
changes bpf_program__attach_{k,u}probe_opts() to use those return
values directly instead of re-reading possibly changed errno.

Signed-off-by: Hoyeon Lee <hoyeon.lee@suse.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20260401143116.185049-2-hoyeon.lee@suse.com