MAINTAINERS: update dpot-dac.yaml reference

Changeset 06d2ff6f ("dt-bindings:iio:dac:dpot-dac: yaml conversion.")
renamed: Documentation/devicetree/bindings/iio/dac/dpot-dac.txt
to: Documentation/devicetree/bindings/iio/dac/dpot-dac.yaml.

Update its cross-reference accordingly.

Fixes: 06d2ff6f ("dt-bindings:iio:dac:dpot-dac: yaml conversion.")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

MAINTAINERS

@@ -8674,7 +8674,7 @@ M:	Peter Rosin <peda@axentia.se>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-iio-dac-dpot-dac
-F:	Documentation/devicetree/bindings/iio/dac/dpot-dac.txt
+F:	Documentation/devicetree/bindings/iio/dac/dpot-dac.yaml
 F:	drivers/iio/dac/dpot-dac.c
 
 IIO ENVELOPE DETECTOR