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.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>