iio: resolver: ad2s1210 add missing select REGMAP in Kconfig

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

Fixes: b3689e14 ("staging: iio: resolver: ad2s1210: use regmap for config registers")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20241003-ad2s1210-select-v1-1-4019453f8c33@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/resolver/Kconfig

@@ -31,6 +31,7 @@ config AD2S1210
 	depends on SPI
 	depends on COMMON_CLK
 	depends on GPIOLIB || COMPILE_TEST
+	select REGMAP
 	help
 	  Say yes here to build support for Analog Devices spi resolver
 	  to digital converters, ad2s1210, provides direct access via sysfs.