[media] reduce poll interval to allow full 60 FPS framerate

[media] reduce poll interval to allow full 60 FPS framerate

The SUR40 hardware can deliver images at up to 60 FPS; at full USB2 bandwidth,
one raw frame will take about 11 ms to transmit. If the poll interval is above
5 ms, fully handling one frame will take longer than 16 ms and the overall
frame rate will drop below 60 FPS. To get the full frame rate without blocking
all the time and still allowing for a bit of timing jitter, we reduce the poll
interval to 4 ms.

Signed-off-by: Martin Kaltenbrunner <modin@yuri.at>
Signed-off-by: Florian Echtler <floe@butterbrot.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>