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.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>