dmaengine: sh: rz-dmac: Avoid format-overflow warning

The max channel count for RZ DMAC is 16, hence use u8 instead of unsigned
int and make the pdev_irqname string long enough to avoid the warning.

This fixes the below issue:
drivers/dma/sh/rz-dmac.c: In function ‘rz_dmac_probe’:
drivers/dma/sh/rz-dmac.c:770:34: warning: ‘%u’ directive writing between 1 and 10 bytes into a region of size 3 [-Wformat-overflow=]
  770 |         sprintf(pdev_irqname, "ch%u", index);
      |                                  ^~
In function ‘rz_dmac_chan_probe’,
    inlined from ‘rz_dmac_probe’ at drivers/dma/sh/rz-dmac.c:910:9:
drivers/dma/sh/rz-dmac.c:770:31: note: directive argument in the range [0, 4294967294]
  770 |         sprintf(pdev_irqname, "ch%u", index);
      |                               ^~~~~~
drivers/dma/sh/rz-dmac.c:770:9: note: ‘sprintf’ output between 4 and 13 bytes into a destination of size 5
  770 |         sprintf(pdev_irqname, "ch%u", index);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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/20240110222717.193719-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: prabhakarlad

drivers/dma/sh/rz-dmac.c

@@ -755,19 +755,19 @@ static struct dma_chan *rz_dmac_of_xlate(struct of_phandle_args *dma_spec,
 
 static int rz_dmac_chan_probe(struct rz_dmac *dmac,
 			      struct rz_dmac_chan *channel,
-			      unsigned int index)
+			      u8 index)
 {
 	struct platform_device *pdev = to_platform_device(dmac->dev);
 	struct rz_lmdesc *lmdesc;
-	char pdev_irqname[5];
+	char pdev_irqname[6];
 	char *irqname;
 	int ret;
 
 	channel->index = index;
 	channel->mid_rid = -EINVAL;
 
 	/* Request the channel interrupt. */
-	sprintf(pdev_irqname, "ch%u", index);
+	scnprintf(pdev_irqname, sizeof(pdev_irqname), "ch%u", index);
 	channel->irq = platform_get_irq_byname(pdev, pdev_irqname);
 	if (channel->irq < 0)
 		return channel->irq;
@@ -845,9 +845,9 @@ static int rz_dmac_probe(struct platform_device *pdev)
 	struct dma_device *engine;
 	struct rz_dmac *dmac;
 	int channel_num;
-	unsigned int i;
 	int ret;
 	int irq;
+	u8 i;
 
 	dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
 	if (!dmac)