MAINTAINERS: update current-sense-shunt.yaml reference

Changeset ce66e52b ("dt-bindings:iio:afe:current-sense-shunt: txt to yaml conversion.")
renamed: Documentation/devicetree/bindings/iio/afe/current-sense-shunt.txt
to: Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml.

Update its cross-reference accordingly.

Fixes: ce66e52b ("dt-bindings:iio:afe:current-sense-shunt: txt to yaml conversion.")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>