Avoid pointlessly calling calc_dphy() when the bus is not
V4L2_MBUS_CSI2_DPHY. This will make it easier to replace the platform data
with devicetree.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>