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

if imx7_csi_try_fmt() fails, outcc variable won't be
initialized and csi->cc[IMX7_CSI_PAD_SRC] would be pointing
to a random location.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>