usb: gadget: uvc: decrease the interrupt load to a quarter

With usb3 we handle many more requests. Decrease the interrupt load by
only enabling the interrupt every quarter of the allocated requests.

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

--
v1 -> v2: - edited patch description
	  - removed extra parantheses
	  - added a comment for the logic
	  - using unsigned int instead of int
	  - reinitializing req_int_count in uvcg_video_enable
v2 -> v3: -
Link: https://lore.kernel.org/r/20210628155311.16762-6-m.grzeschik@pengutronix.de



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