media: i2c: ov5648: Free V4L2 fwnode data on unbind

The V4L2 fwnode data structure doesn't get freed on unbind, which leads to
a memleak.

Fixes: e43ccb0a ("media: i2c: Add support for the OV5648 image sensor")
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Reviewed-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>