test/decode/tinyjpeg: use the fourcc format Y800 for grayscale images

Signed-off-by: Xiang, Haihao <haihao.xiang@intel.com>
Reviewed-by: Beauchesne, Gwenole <gwenole.beauchesne@intel.com>
(cherry picked from commit 62085e11d30db590038a32fffeb04aa8bc0afd67)
1 file changed