iio: core: drop of.h from iio.h

There is no reason to include OF as we only need to forward declare
'of_phandle_args'. Previously, some drivers were actually relying on
this for some headers (those were already fixed).
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220610084545.547700-20-nuno.sa@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/iio/iio.h

@@ -11,13 +11,14 @@
 #include <linux/cdev.h>
 #include <linux/slab.h>
 #include <linux/iio/types.h>
-#include <linux/of.h>
 /* IIO TODO LIST */
 /*
  * Provide means of adjusting timer accuracy.
  * Currently assumes nano seconds.
  */
 
+struct of_phandle_args;
+
 enum iio_shared_by {
 	IIO_SEPARATE,
 	IIO_SHARED_BY_TYPE,