dt-bindings: i2c: google,cros-ec-i2c-tunnel: correct path to i2c-controller schema

dt-bindings: i2c: google,cros-ec-i2c-tunnel: correct path to i2c-controller schema

The referenced i2c-controller.yaml schema is provided by dtschema
package (outside of Linux kernel), so use full path to reference it.

Cc: [email protected]
Fixes: 1acd4577a66f ("dt-bindings: i2c: convert i2c-cros-ec-tunnel to json-schema")
Signed-off-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Signed-off-by: Andi Shyti <[email protected]>