media: doc: pixfmt-rgb: Fix V4L2_PIX_FMT_BGR24 format description

The V4L2_PIX_FMT_BGR24 format is incorrectly described, with the B and G
components swapped. Fix it.

Fixes: 2ac9280c ("media: doc: pixfmt-rgb: Make 8 bits per component table more compact")
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>