media: uvcvideo: Fix incorrect timeout for Get Request

Section 9.2.6.4 of USB 2.0/3.x specification describes that
"device must be able to return the first data packet to host within
500 ms of receipt of the request. For subsequent data packet, if any,
the device must be able to return them within 500 ms".

This is to fix incorrect timeout and change it from 300 ms to 500 ms
to meet the timing specified by specification for Get Request.

Signed-off-by: Jim Lin <jilin@nvidia.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>