dmaengine: ep93xx: Use struct_size()

Use struct_size() instead of hand-writing it, when allocating a structure
with a flex array.

This is less verbose, more robust and more informative.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/36fa11d95b448b5f3f1677da41fe35b9e2751427.1690041500.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: tititiou36

drivers/dma/ep93xx_dma.c

@@ -1320,11 +1320,9 @@ static int __init ep93xx_dma_probe(struct platform_device *pdev)
 	struct ep93xx_dma_platform_data *pdata = dev_get_platdata(&pdev->dev);
 	struct ep93xx_dma_engine *edma;
 	struct dma_device *dma_dev;
-	size_t edma_size;
 	int ret, i;
 
-	edma_size = pdata->num_channels * sizeof(struct ep93xx_dma_chan);
-	edma = kzalloc(sizeof(*edma) + edma_size, GFP_KERNEL);
+	edma = kzalloc(struct_size(edma, channels, pdata->num_channels), GFP_KERNEL);
 	if (!edma)
 		return -ENOMEM;