usb: gadget: uvc: prevent index variables to start from 0

Some configfs variables like bDefaultFrameIndex are always starting by
1. This patch adds a check to prevent setting those variables to 0.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

Link: https://lore.kernel.org/r/20220421211427.3400834-4-m.grzeschik@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/uvc_configfs.c

@@ -1565,6 +1565,12 @@ uvcg_uncompressed_##cname##_store(struct config_item *item,		\
 	if (ret)							\
 		goto end;						\
 									\
+	/* index values in uvc are never 0 */				\
+	if (!num) {							\
+		ret = -EINVAL;						\
+		goto end;						\
+	}								\
+									\
 	u->desc.aname = num;						\
 	ret = len;							\
 end:									\
@@ -1758,6 +1764,12 @@ uvcg_mjpeg_##cname##_store(struct config_item *item,			\
 	if (ret)							\
 		goto end;						\
 									\
+	/* index values in uvc are never 0 */				\
+	if (!num) {							\
+		ret = -EINVAL;						\
+		goto end;						\
+	}								\
+									\
 	u->desc.aname = num;						\
 	ret = len;							\
 end:									\