media: imx: imx7_mipi_csis: Drop csi_state pdev field

The pdev field of the csi_state structure is only used to access the
device pointer, which is stored in a separate field. Drop the pdev
field, as well as a few local dev variables.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>