spi: reorder spi_message struct member doc comments

The members of `struct spi_message` were reordered in commit
ae2ade4b ("spi: Reorder fields in 'struct spi_message'")
but the documentation comments were not updated to match.

This commit updates the comments to match the new order.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://msgid.link/r/20240131170732.1665105-1-dlechner@baylibre.com


Signed-off-by: Mark Brown <broonie@kernel.org>