media: imx: imx7_mipi_csis: Set the CLKSETTLE register field

Set the CLKSETTLE field explicitly, with a value hardcoded to 0. This
brings no functional change, but prepares for calculation of the
CLKSETTLE value.

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>