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>

halleyzhao/libva-fdo,halleyzhao/libva-fdo,CyanogenMod/android_hardware_intel_libva,halleyzhao/libva-fdo,android-ia/hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,android-ia/hardware_intel_libva,CyanogenMod/android_hardware_intel_libva