media: ti-vpe: cal: Get struct device without going through v4l2_device

Instead of retrieving the struct device for the platform device from the
v4l2_device, get it from the platform device directly. This prepares for
cleanups related to v4l2_device handling.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>