iio: dac: ad5770r: add missing select REGMAP_SPI in Kconfig

This driver makes use of regmap_spi, but does not select the required
module.
Add the missing 'select REGMAP_SPI'.

Fixes: cbbb8198 ("iio: dac: ad5770r: Add AD5770R support")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241003-ad2s1210-select-v1-6-4019453f8c33@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/Kconfig

@@ -266,6 +266,7 @@ config AD5766
 config AD5770R
 	tristate "Analog Devices AD5770R IDAC driver"
 	depends on SPI_MASTER
+	select REGMAP_SPI
 	help
 	  Say yes here to build support for Analog Devices AD5770R Digital to
 	  Analog Converter.