dmaengine: mcf-edma: Fix a potential un-allocated memory access

When 'mcf_edma' is allocated, some space is allocated for a
flexible array at the end of the struct. 'chans' item are allocated, that is
to say 'pdata->dma_channels'.

Then, this number of item is stored in 'mcf_edma->n_chans'.

A few lines later, if 'mcf_edma->n_chans' is 0, then a default value of 64
is set.

This ends to no space allocated by devm_kzalloc() because chans was 0, but
64 items are read and/or written in some not allocated memory.

Change the logic to define a default value before allocating the memory.

Fixes: e7a3ff92 ("dmaengine: fsl-edma: add ColdFire mcf5441x edma support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/f55d914407c900828f6fad3ea5fa791a5f17b9a4.1685172449.git.christophe.jaillet@wanadoo.frSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/mcf-edma.c

@@ -190,7 +190,13 @@ static int mcf_edma_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	chans = pdata->dma_channels;
+	if (!pdata->dma_channels) {
+		dev_info(&pdev->dev, "setting default channel number to 64");
+		chans = 64;
+	} else {
+		chans = pdata->dma_channels;
+	}
+
 	len = sizeof(*mcf_edma) + sizeof(*mcf_chan) * chans;
 	mcf_edma = devm_kzalloc(&pdev->dev, len, GFP_KERNEL);
 	if (!mcf_edma)
@@ -202,11 +208,6 @@ static int mcf_edma_probe(struct platform_device *pdev)
 	mcf_edma->drvdata = &mcf_data;
 	mcf_edma->big_endian = 1;
 
-	if (!mcf_edma->n_chans) {
-		dev_info(&pdev->dev, "setting default channel number to 64");
-		mcf_edma->n_chans = 64;
-	}
-
 	mutex_init(&mcf_edma->fsl_edma_mutex);
 
 	mcf_edma->membase = devm_platform_ioremap_resource(pdev, 0);