dt: update a reference for reneases pcar file renamed to yaml

This file was renamed, but its reference at pfc-pinctl.txt is
still pointing to the old file.

Fixes: 7f7d408e ("dt-bindings: gpio: rcar: Convert to json-schema")
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/72d7ec91a60e852d34f3e15bc5faef1f62a8260e.1592203542.git.mchehab+huawei@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pinctrl/renesas,pfc-pinctrl.txt

@@ -114,7 +114,7 @@ with values derived from the SoC user manual.
    [flags]>
 
 On other mach-shmobile platforms GPIO is handled by the gpio-rcar driver.
-Please refer to Documentation/devicetree/bindings/gpio/renesas,gpio-rcar.txt
+Please refer to Documentation/devicetree/bindings/gpio/renesas,rcar-gpio.yaml
 for documentation of the GPIO device tree bindings on those platforms.