dt-bindings: i2c: aspeed: drop redundant multi-master

'multi-master' property is defined by core i2c-controller schema in
dtschema package, so binding which references it and has
unevaluatedProperties:false, does not need to mention it.  It is
completely redundant here.
Suggested-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml

@@ -44,11 +44,6 @@ properties:
     description: frequency of the bus clock in Hz defaults to 100 kHz when not
       specified
 
-  multi-master:
-    type: boolean
-    description:
-      states that there is another master active on this bus
-
 required:
   - reg
   - compatible