bpftool: Properly close va_list 'ap' by va_end() on error

va_list 'ap' was opened but not closed by va_end() in error case. It should
be closed by va_end() before the return.

Fixes: aa52bcb ("tools: bpftool: Fix json dump crash on powerpc")
Signed-off-by: Gu Shengxian <gushengxian@yulong.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/bpf/20210706013543.671114-1-gushengxian507419@gmail.com

Author: Gu Shengxian

tools/bpf/bpftool/jit_disasm.c

@@ -43,11 +43,13 @@ static int fprintf_json(void *out, const char *fmt, ...)
 {
 	va_list ap;
 	char *s;
+	int err;
 
 	va_start(ap, fmt);
-	if (vasprintf(&s, fmt, ap) < 0)
-		return -1;
+	err = vasprintf(&s, fmt, ap);
 	va_end(ap);
+	if (err < 0)
+		return -1;
 
 	if (!oper_count) {
 		int i;