Enabled mpeg2 dxva2 decoding support.

(cherry picked from commit beb86eee)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/avcodec/dxva2.c

@@ -141,7 +141,7 @@ typedef struct {
 } dxva2_mode_t;
 /* XXX Prefered modes must come first */
 static const dxva2_mode_t dxva2_modes[] = {
-    { "DXVA2_ModeMPEG2_VLD",    &DXVA2_ModeMPEG2_VLD,     0 },
+    { "DXVA2_ModeMPEG2_VLD",    &DXVA2_ModeMPEG2_VLD,     CODEC_ID_MPEG2VIDEO },
     { "DXVA2_ModeMPEG2_MoComp", &DXVA2_ModeMPEG2_MoComp,  0 },
     { "DXVA2_ModeMPEG2_IDCT",   &DXVA2_ModeMPEG2_IDCT,    0 },