iio:filter:admv8818: select REGMAP_SPI for ADMV8818

admv8818 driver needs __devm_regmap_init_spi() which is defined
when CONFIG_REGMAP_SPI is set and struct regmap_config when
CONFIG_REGMAP is set, so automatically select CONFIG_REGMAP_SPI
which also sets CONFIG_REGMAP.

Fixes: f34fe88 ("iio:filter:admv8818: add support for ADMV8818")
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220320055457.254983-1-bobo.shaobowang@huawei.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Wang ShaoBo

drivers/iio/filter/Kconfig

@@ -8,6 +8,7 @@ menu "Filters"
 config ADMV8818
 	tristate "Analog Devices ADMV8818 High-Pass and Low-Pass Filter"
 	depends on SPI && COMMON_CLK && 64BIT
+	select REGMAP_SPI
 	help
 	  Say yes here to build support for Analog Devices ADMV8818
 	  2 GHz to 18 GHz, Digitally Tunable, High-Pass and Low-Pass Filter.