MAINTAINERS: update voltage-divider.yaml reference

Changeset 6f633bc9 ("dt-bindings:iio:afe:voltage-divider: txt to yaml conversion")
renamed: Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
to: Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml.

Update its cross-reference accordingly.

Fixes: 6f633bc9 ("dt-bindings:iio:afe:voltage-divider: txt to yaml conversion")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>