greybus: loopback: Fix broken loopback min values

Currently, when a loopback test completely fail,
loopback will return 4294967295 for every min value.
Return 0 instead of 4294967295 in such case.
Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/loopback.c

@@ -148,6 +148,9 @@ static ssize_t name##_##field##_show(struct device *dev,	\
 			    char *buf)					\
 {									\
 	struct gb_loopback *gb = dev_get_drvdata(dev);			\
+	/* Report 0 for min and max if no transfer successed */		\
+	if (!gb->requests_completed)					\
+		return sprintf(buf, "0\n");				\
 	return sprintf(buf, "%"#type"\n", gb->name.field);	\
 }									\
 static DEVICE_ATTR_RO(name##_##field)