usb: gadget: uvc: only schedule stream in streaming state

usb: gadget: uvc: only schedule stream in streaming state

This patch ensures that the video pump thread will only be scheduled if
the uvc is really in streaming state. This way the worker will not have
to run on an empty queue.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Link: https://lore.kernel.org/r/20211017215017.18392-5-m.grzeschik@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>