Fix return value in trailing_strtoln()

This function should return -1 if there is no trailing integer in the
string. Instead it returns 0. Fix it by checking for this condition at the
start.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

lib/strto.c

@@ -160,9 +160,11 @@ long trailing_strtoln(const char *str, const char *end)
 
 	if (!end)
 		end = str + strlen(str);
-	for (p = end - 1; p > str; p--) {
-		if (!isdigit(*p))
-			return simple_strtoul(p + 1, NULL, 10);
+	if (isdigit(end[-1])) {
+		for (p = end - 1; p > str; p--) {
+			if (!isdigit(*p))
+				return simple_strtoul(p + 1, NULL, 10);
+		}
 	}
 
 	return -1;