media: imx7-media-csi: don't store a floating pointer

if imx7_csi_try_fmt() fails, cc variable won't be
initialized and csi->cc[sdformat->pad] would be pointing
to a random location.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>