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: 0a024d63 ("[media] ov7670: get xclk")

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

drivers/media/i2c/ov7670.c

@@ -1808,9 +1808,15 @@ 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);
+	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;
@@ -1820,6 +1826,7 @@ static int ov7670_probe(struct i2c_client *client,
 			ret = -EINVAL;
 			goto clk_disable;
 		}
+	}
 
 	ret = ov7670_init_gpio(client, info);
 	if (ret)