[media] exynos4-is: Fix fimc_is_parse_sensor_config() nodes handling

The same struct device_node * is used for looking up the I2C sensor, OF
graph endpoint and port. So the reference count is incremented but not
decremented for the endpoint and port nodes.

Fix this by having separate pointers for each node looked up.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Nicolas Dufresne <nicoas.dufresne@collabora.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>