dmaengine: at_hdmac: fix module unloading

BugLink: https://bugs.launchpad.net/bugs/1811077

commit 77e75fda upstream.

of_dma_controller_free() was not called on module onloading.
This lead to a soft lockup:
watchdog: BUG: soft lockup - CPU#0 stuck for 23s!
Modules linked in: at_hdmac [last unloaded: at_hdmac]
when of_dma_request_slave_channel() tried to call ofdma->of_dma_xlate().

Cc: stable@vger.kernel.org
Fixes: bbe89c8e ("at_hdmac: move to generic DMA binding")
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/dma/at_hdmac.c

@@ -2152,6 +2152,8 @@ static int at_dma_remove(struct platform_device *pdev)
 	struct resource		*io;
 
 	at_dma_off(atdma);
+	if (pdev->dev.of_node)
+		of_dma_controller_free(pdev->dev.of_node);
 	dma_async_device_unregister(&atdma->dma_common);
 
 	dma_pool_destroy(atdma->memset_pool);