regulator: anatop: make regulator name property required

We actually can't allow the missing of the regualor name, thus update
the binding doc to make regulator-name property to be required.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/anatop-regulator.txt

@@ -2,6 +2,7 @@ Anatop Voltage regulators
 
 Required properties:
 - compatible: Must be "fsl,anatop-regulator"
+- regulator-name: A string used as a descriptive name for regulator outputs
 - anatop-reg-offset: Anatop MFD register offset
 - anatop-vol-bit-shift: Bit shift for the register
 - anatop-vol-bit-width: Number of bits used in the register