iio: adc: ti-lmp92064: 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: 62719894 ("iio: adc: add ADC driver for the TI LMP92064 controller")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241003-iio-select-v1-5-67c0385197cd@gmail.com


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>