linux-imx

dmaengine: mxs-dma: use dmaenginem_async_device_register to simplify the code

Use dmaenginem_async_device_register to simplify the code:
	remove dma_async_device_unregister.

Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai>
Signed-off-by: Vinod Koul <vkoul@kernel.org>