dmaengine: at_hdmac: check return value of of_find_device_by_node() in at_dma_xlate()

dmaengine: at_hdmac: check return value of of_find_device_by_node() in at_dma_xlate()

[ Upstream commit 0cef8e2c5a07d482ec907249dbd6687e8697677f ]

The reurn value of of_find_device_by_node() is not checked, thus null
pointer dereference will be triggered if of_find_device_by_node()
failed.

Fixes: bbe89c8e3d59 ("at_hdmac: move to generic DMA binding")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20200817115728.1706719-2-yukuai3@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>