[media] gspca - kinect: move communications buffers out of stack

Move large communications buffers out of stack and into device
structure. This prevents the frame size from being >1kB and fixes a
compiler warning when CONFIG_FRAME_WARN=1024:

drivers/media/video/gspca/kinect.c: In function ‘send_cmd.clone.0’:
drivers/media/video/gspca/kinect.c:202: warning: the frame size of 1548 bytes is larger than 1024 bytes

Reported-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Drew Fisher <drew.m.fisher@gmail.com>
Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>