iio: Add resource managed APIs devm_iio_channel_{get,release) in devres

Add following APIs in the list of managed resources of IIO:
	devm_iio_channel_get()
	devm_iio_channel_get_all()
	devm_iio_channel_release()
	devm_iio_channel_release_all()

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/driver-model/devres.txt

@@ -267,6 +267,10 @@ IIO
   devm_iio_kfifo_free()
   devm_iio_trigger_alloc()
   devm_iio_trigger_free()
+  devm_iio_channel_get()
+  devm_iio_channel_release()
+  devm_iio_channel_get_all()
+  devm_iio_channel_release_all()
 
 IO region
   devm_release_mem_region()