dmaengine: hisilicon: Use struct_size() in devm_kzalloc()

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

This code was detected with the help of Coccinelle and, audited and
fixed manually.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Zhou Wang <wangzhou1@hisilicon.com>
Link: https://lore.kernel.org/r/20200617211135.GA8660@embeddedorSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/hisi_dma.c

@@ -511,7 +511,6 @@ static int hisi_dma_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	struct device *dev = &pdev->dev;
 	struct hisi_dma_dev *hdma_dev;
 	struct dma_device *dma_dev;
-	size_t dev_size;
 	int ret;
 
 	ret = pcim_enable_device(pdev);
@@ -534,9 +533,7 @@ static int hisi_dma_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (ret)
 		return ret;
 
-	dev_size = sizeof(struct hisi_dma_chan) * HISI_DMA_CHAN_NUM +
-		   sizeof(*hdma_dev);
-	hdma_dev = devm_kzalloc(dev, dev_size, GFP_KERNEL);
+	hdma_dev = devm_kzalloc(dev, struct_size(hdma_dev, chan, HISI_DMA_CHAN_NUM), GFP_KERNEL);
 	if (!hdma_dev)
 		return -EINVAL;