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)
diff --git a/test/decode/tinyjpeg.c b/test/decode/tinyjpeg.c
index 0a544fe..33dcdc6 100644
--- a/test/decode/tinyjpeg.c
+++ b/test/decode/tinyjpeg.c
@@ -693,7 +693,7 @@
        else
        {
            surface_type = VA_RT_FORMAT_YUV400;
-           forcc.value.value.i = VA_FOURCC('4','0','0','P');
+           forcc.value.value.i = VA_FOURCC('Y','8','0','0');
            ChromaTypeIndex = 0;
            type = "Format_400P";
        }