bpf: btf: Fix vsnprintf return value check

vsnprintf returns the number of characters which would have been written if
enough space had been available, excluding the terminating null byte. Thus,
the return value of 'len_left' means that the last character has been
dropped.
Signed-off-by: Fedor Tokarev <ftokarev@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20220711211317.GA1143610@laptop

kernel/bpf/btf.c

@@ -6643,7 +6643,7 @@ static void btf_snprintf_show(struct btf_show *show, const char *fmt,
 	if (len < 0) {
 		ssnprintf->len_left = 0;
 		ssnprintf->len = len;
-	} else if (len > ssnprintf->len_left) {
+	} else if (len >= ssnprintf->len_left) {
 		/* no space, drive on to get length we would have written */
 		ssnprintf->len_left = 0;
 		ssnprintf->len += len;