media: stm32: dcmi: Fix subdev op call with uninitialized state

stm32-dcmi calls its source subdev with v4l2_subdev_call() using a
v4l2_subdev_state constructed on stack. This means that init_cfg is
never called for that state, and a source subdev that depends on the
init_cfg call may break.

A new macro has been added for this particular purpose, which properly
initializes the state, so let's use v4l2_subdev_call_state_try() here.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>