[media] DocBook media: fix PIX_FMT_SGRBR8 example

Fix the example of the V4L2_PIX_FMT_SGRBG8 Bayer format.

The even lines should read BGBG, not RBRB.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>