[media] si4713: add device tree support

Add device tree support by changing the device registration order.
In the device tree the si4713 node is a normal I2C device, which
will be probed as such. Thus the V4L device must be probed from
the I2C device and not the other way around.

Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>