media: ov5670: Fix probe on ACPI

devm_clk_get() will return either an error or NULL, which the driver
handles, continuing to use the clock of reading the value of the
clock-frequency property.

However, the value of ov5670->xvclk is left as-is and the other clock
framework functions aren't capable of handling error values.

Use devm_clk_get_optional() to obtain NULL instead of -ENOENT.

Fixes: 8004c91 ("media: i2c: ov5670: Use common clock framework")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Author: Sakari Ailus

drivers/media/i2c/ov5670.c

@@ -2691,7 +2691,7 @@ static int ov5670_probe(struct i2c_client *client)
 	if (!ov5670)
 		return -ENOMEM;
 
-	ov5670->xvclk = devm_clk_get(&client->dev, NULL);
+	ov5670->xvclk = devm_clk_get_optional(&client->dev, NULL);
 	if (!IS_ERR_OR_NULL(ov5670->xvclk))
 		input_clk = clk_get_rate(ov5670->xvclk);
 	else if (!ov5670->xvclk || PTR_ERR(ov5670->xvclk) == -ENOENT)