media: ov7670: make "xclk" clock optional

When the "xclk" clock was added, it was made mandatory. This broke the
driver on an OLPC plaform which doesn't know such clock. Make it
optional.

Tested on a OLPC XO-1 laptop.

Fixes: 0a024d634c ("[media] ov7670: get xclk")

Cc: stable@vger.kernel.org # 4.11+
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/i2c/ov7670.c

@@ -1808,17 +1808,24 @@ static int ov7670_probe(struct i2c_client *client,
 			info->pclk_hb_disable = true;
 	}
 
-	info->clk = devm_clk_get(&client->dev, "xclk");
-	if (IS_ERR(info->clk))
-		return PTR_ERR(info->clk);
-	ret = clk_prepare_enable(info->clk);
-	if (ret)
-		return ret;
+	info->clk = devm_clk_get(&client->dev, "xclk"); /* optional */
+	if (IS_ERR(info->clk)) {
+		ret = PTR_ERR(info->clk);
+		if (ret == -ENOENT)
+			info->clk = NULL;
+		else
+			return ret;
+	}
+	if (info->clk) {
+		ret = clk_prepare_enable(info->clk);
+		if (ret)
+			return ret;
 
-	info->clock_speed = clk_get_rate(info->clk) / 1000000;
-	if (info->clock_speed < 10 || info->clock_speed > 48) {
-		ret = -EINVAL;
-		goto clk_disable;
+		info->clock_speed = clk_get_rate(info->clk) / 1000000;
+		if (info->clock_speed < 10 || info->clock_speed > 48) {
+			ret = -EINVAL;
+			goto clk_disable;
+		}
 	}
 
 	ret = ov7670_init_gpio(client, info);