Use dmaenginem_async_device_register to simplify the code:
	remove dma_async_device_unregister.
Acked-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai>
Signed-off-by: Vinod Koul <vkoul@kernel.org>