dt-bindings: iio: imu: mpu6050: add vdd-supply

inv_mpu6050 now supports an additional vdd-supply; document it.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/imu/inv_mpu6050.txt

@@ -21,6 +21,7 @@ Required properties:
   bindings.
 
 Optional properties:
+ - vdd-supply: regulator phandle for VDD supply
  - vddio-supply: regulator phandle for VDDIO supply
  - mount-matrix: an optional 3x3 mounting rotation matrix
  - i2c-gate node.  These devices also support an auxiliary i2c bus.  This is