iio: adc: ingenic-adc: explicitly add proper header files

Do not trust the fact that iio.h includes of.h which in turn includes
all the headers we are relying on.

The ultimate goal is to actually drop of.h from iio.h.
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220610084545.547700-7-nuno.sa@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ingenic-adc.c

@@ -17,7 +17,9 @@
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
 #include <linux/mutex.h>
+#include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/property.h>
 
 #define JZ_ADC_REG_ENABLE		0x00
 #define JZ_ADC_REG_CFG			0x04