MAINTAINERS: add include/dt-bindings/iio to IIO SUBSYSTEM AND DRIVERS

Maintainers of the directory Documentation/devicetree/bindings/iio
are also the maintainers of the corresponding directory
include/dt-bindings/iio.

Add the file entry for include/dt-bindings/iio to the appropriate
section in MAINTAINERS.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20220613115045.24326-1-lukas.bulwahn@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -9607,6 +9607,7 @@ F:	Documentation/ABI/testing/sysfs-bus-iio*
 F:	Documentation/devicetree/bindings/iio/
 F:	drivers/iio/
 F:	drivers/staging/iio/
+F:	include/dt-bindings/iio/
 F:	include/linux/iio/
 F:	tools/iio/