media: verisilicon: Get bit depth for V4L2_PIX_FMT_NV15_4L4

Let's the driver knows that V4L2_PIX_FMT_NV15_4L4 is a 10bits
pixel format.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>