iio:light:ltr501: fix regmap dependency

The use of regmap in commit 2f2c963 requires REGMAP_I2C to be selected, in
order to meet all dependencies.

Fixes: 2f2c963 ("iio: ltr501: Add regmap support.")

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Acked-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/light/Kconfig

@@ -188,6 +188,7 @@ config SENSORS_LM3533
 config LTR501
 	tristate "LTR-501ALS-01 light sensor"
 	depends on I2C
+	select REGMAP_I2C
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 	help