power: supply: mt6370: uses IIO interfaces, depends on IIO

The mt6370-charger driver uses IIO interfaces and produces build
errors when CONFIG_IIO is not set, so it should depend on IIO.

ERROR: modpost: "iio_read_channel_processed" [drivers/power/supply/mt6370-charger.ko] undefined!
ERROR: modpost: "devm_iio_channel_get_all" [drivers/power/supply/mt6370-charger.ko] undefined!

Fixes: 233cb8a4 ("power: supply: mt6370: Add MediaTek MT6370 charger driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: ChiaEn Wu <chiaen_wu@richtek.com>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Cc: linux-pm@vger.kernel.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/Kconfig

@@ -623,6 +623,7 @@ config CHARGER_MT6370
 	tristate "MediaTek MT6370 Charger Driver"
 	depends on MFD_MT6370
 	depends on REGULATOR
+	depends on IIO
 	select LINEAR_RANGES
 	help
 	  Say Y here to enable MT6370 Charger Part.