dt-bindings: stm32-dma: Fix typo regarding DMA client binding

Only four cells are required for dma client binding not five.

Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Reviewed-by: Ludovic BARRE <ludovic.barre@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>