[media] DocBook: v4l: Fix raw bayer pixel format documentation wording

The documentation began with "The following four pixel formats"... but the
format definitions preceded this sentence. Replace it with "These four pixel
formats".

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>