media: imx: imx-mipi-csis: Rename csi_state to mipi_csis_device

Usage of "state" for the device-specific data structure is confusing, as
it can also refer to the subdev state. Rename the structure to
mipi_csis_device, and the corresponding state variables to csis.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>