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

Signed-off-by: Xiang, Haihao <8d677183e5993577d4fa73a419b76987913292d6@intel.com>
Reviewed-by: Beauchesne, Gwenole <729713629d9640cc095f1c77c692e1881f8093c4@intel.com>
(cherry picked from commit 62085e11d30db590038a32fffeb04aa8bc0afd67)

gbeauchesne/libva,gbeauchesne/libva,gbeauchesne/libva