dt-bindings: mfd: Fix path to atmel/hlcdc-dc.txt

Atmel hlcdc-dc documentation is actually in
Documentation/devicetree/bindings/display/atmel/hlcdc-dc.txt

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/mfd/atmel-hlcdc.txt

@@ -15,7 +15,7 @@ Required properties:
 
 The HLCDC IP exposes two subdevices:
  - a PWM chip: see ../pwm/atmel-hlcdc-pwm.txt
- - a Display Controller: see ../display/atmel-hlcdc-dc.txt
+ - a Display Controller: see ../display/atmel/hlcdc-dc.txt
 
 Example: