iio: accel: kxsd9: Convert to use regmap for transport

This converts the KXSD9 driver to drop the custom transport
mechanism and just use regmap like everything else.

Tested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
index 89bc5c5..eebc20d 100644
--- a/drivers/iio/accel/Kconfig
+++ b/drivers/iio/accel/Kconfig
@@ -131,6 +131,7 @@
 	depends on KXSD9
 	depends on SPI
 	default KXSD9
+	select REGMAP_SPI
 	help
 	  Say yes here to enable the Kionix KXSD9 accelerometer
 	  SPI transport channel.