dmaengine: stm32-mdma: use dmaenginem_async_device_register to simplify the code

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>

drivers/dma/stm32-mdma.c

@@ -1656,7 +1656,7 @@ static int stm32_mdma_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	ret = dma_async_device_register(dd);
+	ret = dmaenginem_async_device_register(dd);
 	if (ret)
 		return ret;
 
@@ -1674,8 +1674,6 @@ static int stm32_mdma_probe(struct platform_device *pdev)
 	return 0;
 
 err_unregister:
-	dma_async_device_unregister(dd);
-
 	return ret;
 }