dt-bindings: mmc: Fix 'dma-coherent' was unexpected

dma-coherent is mentioned in almost all TI K3 platform mmc
nodes. Fix warning generated due to its missing match in
yaml schema.
Signed-off-by: Apurva Nandan <a-nandan@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220819190729.32358-3-a-nandan@ti.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

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

@@ -51,6 +51,9 @@ properties:
 
   sdhci-caps-mask: true
 
+  dma-coherent:
+    type: boolean
+
   # PHY output tap delays:
   # Used to delay the data valid window and align it to the sampling clock.
   # Binding needs to be provided for each supported speed mode otherwise the