V4L/DVB: uvcvideo: Add support for V4L2_PIX_FMT_Y16

The Miricle 307K (17dc:0202) camera reports a 16-bit greyscale format,
support it in the driver.

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