media: imx: imx7-media-csi: fix missing clk_disable_unprepare() in imx7_csi_init()

Add missing clk_disable_unprepare(), if imx7_csi_dma_setup() fails
in imx7_csi_init().

Fixes: ff43ca91 ("media: imx: imx7-media-csi: Move CSI configuration before source start")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>