dmaengine: at_xdmac: 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 or integer overflows that, in
the worst scenario, could lead to heap overflows.

Link: https://github.com/KSPP/linux/issues/160Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20211208001013.GA62330@embeddedorSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/at_xdmac.c

@@ -2031,7 +2031,7 @@ static int __maybe_unused atmel_xdmac_resume(struct device *dev)
 static int at_xdmac_probe(struct platform_device *pdev)
 {
 	struct at_xdmac	*atxdmac;
-	int		irq, size, nr_channels, i, ret;
+	int		irq, nr_channels, i, ret;
 	void __iomem	*base;
 	u32		reg;
 
@@ -2056,9 +2056,9 @@ static int at_xdmac_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	size = sizeof(*atxdmac);
-	size += nr_channels * sizeof(struct at_xdmac_chan);
-	atxdmac = devm_kzalloc(&pdev->dev, size, GFP_KERNEL);
+	atxdmac = devm_kzalloc(&pdev->dev,
+			       struct_size(atxdmac, chan, nr_channels),
+			       GFP_KERNEL);
 	if (!atxdmac) {
 		dev_err(&pdev->dev, "can't allocate at_xdmac structure\n");
 		return -ENOMEM;