dmaengine: usb-dmac: Avoid format-overflow warning

gcc points out that the fix-byte buffer might be too small:
drivers/dma/sh/usb-dmac.c: In function 'usb_dmac_probe':
drivers/dma/sh/usb-dmac.c:720:34: warning: '%u' directive writing between 1 and 10 bytes into a region of size 3 [-Wformat-overflow=]
  720 |         sprintf(pdev_irqname, "ch%u", index);
      |                                  ^~
In function 'usb_dmac_chan_probe',
    inlined from 'usb_dmac_probe' at drivers/dma/sh/usb-dmac.c:814:9:
drivers/dma/sh/usb-dmac.c:720:31: note: directive argument in the range [0, 4294967294]
  720 |         sprintf(pdev_irqname, "ch%u", index);
      |                               ^~~~~~
drivers/dma/sh/usb-dmac.c:720:9: note: 'sprintf' output between 4 and 13 bytes into a destination of size 5
  720 |         sprintf(pdev_irqname, "ch%u", index);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Maximum number of channels for USB-DMAC as per the driver is 1-99 so use
u8 instead of unsigned int/int for DMAC channel indexing and make the
pdev_irqname string long enough to avoid the warning.

While at it use scnprintf() instead of sprintf() to make the code more
robust.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20240110222210.193479-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: prabhakarlad

drivers/dma/sh/usb-dmac.c

@@ -706,18 +706,18 @@ static const struct dev_pm_ops usb_dmac_pm = {
 
 static int usb_dmac_chan_probe(struct usb_dmac *dmac,
 			       struct usb_dmac_chan *uchan,
-			       unsigned int index)
+			       u8 index)
 {
 	struct platform_device *pdev = to_platform_device(dmac->dev);
-	char pdev_irqname[5];
+	char pdev_irqname[6];
 	char *irqname;
 	int ret;
 
 	uchan->index = index;
 	uchan->iomem = dmac->iomem + USB_DMAC_CHAN_OFFSET(index);
 
 	/* Request the channel interrupt. */
-	sprintf(pdev_irqname, "ch%u", index);
+	scnprintf(pdev_irqname, sizeof(pdev_irqname), "ch%u", index);
 	uchan->irq = platform_get_irq_byname(pdev, pdev_irqname);
 	if (uchan->irq < 0)
 		return -ENODEV;
@@ -768,8 +768,8 @@ static int usb_dmac_probe(struct platform_device *pdev)
 	const enum dma_slave_buswidth widths = USB_DMAC_SLAVE_BUSWIDTH;
 	struct dma_device *engine;
 	struct usb_dmac *dmac;
-	unsigned int i;
 	int ret;
+	u8 i;
 
 	dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
 	if (!dmac)
@@ -869,7 +869,7 @@ static void usb_dmac_chan_remove(struct usb_dmac *dmac,
 static void usb_dmac_remove(struct platform_device *pdev)
 {
 	struct usb_dmac *dmac = platform_get_drvdata(pdev);
-	int i;
+	u8 i;
 
 	for (i = 0; i < dmac->n_channels; ++i)
 		usb_dmac_chan_remove(dmac, &dmac->channels[i]);