spi: Move comment about chipselect check to the right place

The part of the comment about locking isn't that relevant compared to
the chip select check. So drop the sentence about locking.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211007121415.2401638-2-u.kleine-koenig@pengutronix.de


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