libbpf: Fix memory leak in btf__dedup()

Free btf_dedup if btf_ensure_modifiable() returns error.

Fixes: 919d2b1d ("libbpf: Allow modification of BTF and add btf__add_str API")
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211022202035.48868-1-mauricio@kinvolk.io

tools/lib/bpf/btf.c

@@ -2991,8 +2991,10 @@ int btf__dedup(struct btf *btf, struct btf_ext *btf_ext,
 		return libbpf_err(-EINVAL);
 	}
 
-	if (btf_ensure_modifiable(btf))
-		return libbpf_err(-ENOMEM);
+	if (btf_ensure_modifiable(btf)) {
+		err = -ENOMEM;
+		goto done;
+	}
 
 	err = btf_dedup_prep(d);
 	if (err) {