media: imx-mipi-csis: Shorten name of subdev state variables

media: imx-mipi-csis: Shorten name of subdev state variables

Rename sd_state to state to standardize the naming of the subdev state
variables and help shortening lines.

No functional change is intended.

Link: https://lore.kernel.org/r/20250822002734.23516-5-laurent.pinchart@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>