media: uapi: Clarify MBUS color component order for serial buses

Upstream series https://lore.kernel.org/linux-media/20250917-csi-bgr-rgb-v3-0-0145571b3aa4@kernel.org/

The subdev format documentation has a subsection describing how to use
the media bus pixel codes for serial buses. While it describes the
sampling part well, it doesn't really describe the current convention
used for the components order.

Let's improve that.

Signed-off-by: Maxime Ripard <mripard@kernel.org>

Author: mripard

Documentation/userspace-api/media/v4l/subdev-formats.rst

@@ -160,12 +160,14 @@ correspondence between them.
 
 The media bus pixel codes document parallel formats. Should the pixel data be
 transported over a serial bus, the media bus pixel code that describes a
-parallel format that transfers a sample on a single clock cycle is used. For
-instance, both MEDIA_BUS_FMT_BGR888_1X24 and MEDIA_BUS_FMT_BGR888_3X8 are used
-on parallel busses for transferring an 8 bits per sample BGR data, whereas on
-serial busses the data in this format is only referred to using
-MEDIA_BUS_FMT_BGR888_1X24. This is because there is effectively only a single
-way to transport that format on the serial busses.
+parallel format that transfers a sample on a single clock cycle is used. The
+color component order used is the same used on the serial bus. For instance,
+both MEDIA_BUS_FMT_BGR888_1X24 and MEDIA_BUS_FMT_BGR888_3X8 are used on parallel
+busses for transferring an 8 bits per sample BGR data, whereas on serial busses
+the data in this format is only referred to using MEDIA_BUS_FMT_BGR888_1X24,
+with BGR meaning that the blue component is transmitted first, then green, then
+red. This is because there is effectively only a single way to transport that
+format on the serial busses.
 
 Packed RGB Formats
 ^^^^^^^^^^^^^^^^^^