leds: renesas-tpu: Improve the readability to pick the lowest acceptable rate

I spent a few minutes to understand why the code catching the mismatch case
by checking if k is 0 or not. And the code using "k - 1" as array index is
unusual.

This patch checks acceptable rate from the lowest rate, and then we don't need
to subtract k by 1. This change improves the readability.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

drivers/leds/leds-renesas-tpu.c

@@ -133,24 +133,24 @@ static int r_tpu_enable(struct r_tpu_priv *p, enum led_brightness brightness)
 	rate = clk_get_rate(p->clk);
 
 	/* pick the lowest acceptable rate */
-	for (k = 0; k < ARRAY_SIZE(prescaler); k++)
-		if ((rate / prescaler[k]) < p->min_rate)
+	for (k = ARRAY_SIZE(prescaler) - 1; k >= 0; k--)
+		if ((rate / prescaler[k]) >= p->min_rate)
 			break;
 
-	if (!k) {
+	if (k < 0) {
 		dev_err(&p->pdev->dev, "clock rate mismatch\n");
 		goto err0;
 	}
 	dev_dbg(&p->pdev->dev, "rate = %lu, prescaler %u\n",
-		rate, prescaler[k - 1]);
+		rate, prescaler[k]);
 
 	/* clear TCNT on TGRB match, count on rising edge, set prescaler */
-	r_tpu_write(p, TCR, 0x0040 | (k - 1));
+	r_tpu_write(p, TCR, 0x0040 | k);
 
 	/* output 0 until TGRA, output 1 until TGRB */
 	r_tpu_write(p, TIOR, 0x0002);
 
-	rate /= prescaler[k - 1] * p->refresh_rate;
+	rate /= prescaler[k] * p->refresh_rate;
 	r_tpu_write(p, TGRB, rate);
 	dev_dbg(&p->pdev->dev, "TRGB = 0x%04lx\n", rate);