Documentation: devres: Add missing INPUT function

devm_input_allocate_device() got introduced with commit 2be975c6d920
("Input: introduce managed input devices (add devres support)").
Add this function to the list of managed interfaces within the
devres documentation.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-model/devres.txt

@@ -268,6 +268,9 @@ IIO
   devm_iio_trigger_alloc()
   devm_iio_trigger_free()
 
+INPUT
+  devm_input_allocate_device()
+
 IO region
   devm_release_mem_region()
   devm_release_region()