V4L/DVB (10296): uvcvideo: Fix memory leak in input device handling

The dynamically allocated input_dev->phys buffer isn't freed when
unregistering the device. As the input layer doesn't provide any release
callback, use a fixed-size buffer inside the uvc_device structure.

Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>