dt-bindings: input: iqs7222: Use central 'linux,code' definition

Channel events adopt the newly centralized 'linux,code' property;
slider events should too.

Fixes: 8ac14d2c ("dt-bindings: input: Centralize 'linux,code' definition")
Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220710024713.17275-1-jeff@labundy.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>