media: dt-bindings: nokia,smia: Make vana-supply optional

vana-supply is optional in the spec, therefore make it optional in
bindings, too.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/devicetree/bindings/media/i2c/nokia,smia.txt

@@ -16,8 +16,6 @@ Mandatory properties
 
 - compatible: "nokia,smia"
 - reg: I2C address (0x10, or an alternative address)
-- vana-supply: Analogue voltage supply (VANA), typically 2,8 volts (sensor
-  dependent).
 - clocks: External clock to the sensor
 - clock-frequency: Frequency of the external clock to the sensor
 
@@ -31,6 +29,8 @@ Optional properties
 - rotation: Integer property; valid values are 0 (sensor mounted upright)
 	    and 180 (sensor mounted upside down). See
 	    ../video-interfaces.txt .
+- vana-supply: Analogue voltage supply (VANA), typically 2,8 volts (sensor
+  dependent).
 
 
 Endpoint node mandatory properties