media: ov2680: Clear the 'ret' variable on success

Since commit 63b0cd30 ("media: ov2680: Add bus-cfg / endpoint
property verification") even when the correct 'link-frequencies'
property is passed in the devicetree, the driver fails to probe:

ov2680 1-0036: probe with driver ov2680 failed with error -22

The reason is that the variable 'ret' may contain the -EINVAL value
from a previous assignment:

ret = fwnode_property_read_u32(dev_fwnode(dev), "clock-frequency",
			       &rate);

Fix the problem by clearing 'ret' on the successful path.

Tested on imx7s-warp board with the following devicetree:

port {
	ov2680_to_mipi: endpoint {
		remote-endpoint = <&mipi_from_sensor>;
		clock-lanes = <0>;
		data-lanes = <1>;
		link-frequencies = /bits/ 64 <330000000>;
	};
};

Cc: stable@vger.kernel.org
Fixes: 63b0cd30 ("media: ov2680: Add bus-cfg / endpoint property verification")
Suggested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>