spi: atmel: Remove and fix erroneous comments

Since CSAAT functionality support has been added. Some comments become
wrong. Fix them to match the current driver behavior.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20191017141846.7523-2-gregory.clement@bootlin.com


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