media: doc: pixfmt-yuv: Fix V4L2-PIX-FMT-Y10P format

This packed grey-scale image format has a depth of 10 bits per pixel.
Every four consecutive pixels are packed into 5 bytes. Each of the first
4 bytes contain the 8 high order bits of the pixels, and the 5th byte
contains the 2 least significants bits of each pixel, in the same order.

The first two bytes are not corresponding to this description, fix it.

Fixes: af4f4505 ("media: doc: pixfmt-yuv: Move all luma-only YUV formats to common file")
Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>