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 <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

include/linux/iio/iio.h

···
 #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,