dmaengine: stm32-dma: Set correct args number for DMA request from DT

This patch sets the right number of arguments to be used for DMA clients
which request channels from DT.

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