MAINTAINERS: update renesas,rcar-gyroadc.yaml reference

Changeset 8c412458 ("dt-bindings:iio:adc:renesas,rcar-gyroadc: txt to yaml conversion.")
renamed: Documentation/devicetree/bindings/iio/adc/renesas,gyroadc.txt
to: Documentation/devicetree/bindings/iio/adc/renesas,rcar-gyroadc.yaml.

Update its cross-reference accordingly.

Fixes: 8c412458 ("dt-bindings:iio:adc:renesas,rcar-gyroadc: txt to yaml conversion.")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>