media: rcar-csi2: Set bus type when parsing fwnode

The only supported bus for the R-Car CSI-2 driver is CSI-2 DPHY, specify
this before parsing the fwnode.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>