dt-bindings: input: touchscreen: tsc2007: document '#io-channel-cells'

The tsc2007 can be used not only as resistive touchscreen controller but
also as a ADC IIO sensor. The second use case requires '#io-channel-cells'
property, hence add it.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260122193549.29858-2-clamor95@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: clamor-s

Documentation/devicetree/bindings/input/touchscreen/ti,tsc2007.yaml

@@ -53,6 +53,9 @@ properties:
       how much time to wait (in milliseconds) before reading again the
       values from the tsc2007.
 
+  "#io-channel-cells":
+    const: 1
+
 required:
   - compatible
   - reg