libbpf: fix memory leak in attach_tp for target-less tracepoint program

Fix sec_name memory leak if user defines target-less SEC("tp").

Fixes: 9af8efc4

 ("libbpf: Allow "incomplete" basic tracing SEC() definitions")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20220516184547.3204674-1-andrii@kernel.org


Signed-off-by: Alexei Starovoitov <ast@kernel.org>