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: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

lib/strto.c

@@ -160,10 +160,12 @@ long trailing_strtoln(const char *str, const char *end)
 
 	if (!end)
 		end = str + strlen(str);
+	if (isdigit(end[-1])) {
 		for (p = end - 1; p > str; p--) {
 			if (!isdigit(*p))
 				return simple_strtoul(p + 1, NULL, 10);
 		}
+	}
 
 	return -1;
 }