dt-bindings: mmc: am654: Simplify dma-coherent property

Common boolean properties need to be only allowed in the binding
(":true"), because their type is already defined by core DT schema.
Simplify dma-coherent property to match common syntax.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: krzk

Documentation/devicetree/bindings/mmc/sdhci-am654.yaml

@@ -50,8 +50,7 @@ properties:
       - const: clk_ahb
       - const: clk_xin
 
-  dma-coherent:
-    type: boolean
+  dma-coherent: true
 
   # PHY output tap delays:
   # Used to delay the data valid window and align it to the sampling clock.