dt-bindings:iio:dac: update microchip,mcp4725.yaml reference

Changeset 6ced946a4bba ("dt-bindings:iio:dac:microchip,mcp4725 yaml conversion")
renamed: Documentation/devicetree/bindings/iio/dac/mcp4725.txt
to: Documentation/devicetree/bindings/iio/dac/microchip,mcp4725.yaml.

Update its cross-reference accordingly.

Fixes: 6ced946a4bba ("dt-bindings:iio:dac:microchip,mcp4725 yaml conversion")
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Link: https://lore.kernel.org/r/82fb54[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

include/linux/iio/dac/mcp4725.h

···
  * @vref_buffered: Controls buffering of the external reference voltage.
  *
  * Vref related settings are available only on MCP4756. See
- * Documentation/devicetree/bindings/iio/dac/mcp4725.txt for more information.
+ * Documentation/devicetree/bindings/iio/dac/microchip,mcp4725.yaml for more information.
  */
 struct mcp4725_platform_data {
 	bool use_vref;