Add the H.264 decoder as a dependency for the fate-mkv test.

tests/fate/demux.mak

@@ -40,7 +40,7 @@ fate-lmlm4-demux: CMD = framecrc -i $(TARGET_SAMPLES)/lmlm4/LMLM4_CIFat30fps.div
 FATE_SAMPLES_DEMUX-$(CONFIG_XA_DEMUXER) += fate-maxis-xa
 fate-maxis-xa: CMD = framecrc -i $(TARGET_SAMPLES)/maxis-xa/SC2KBUG.XA -frames:a 30 -c:a copy
 
-FATE_SAMPLES_DEMUX-$(CONFIG_MATROSKA_DEMUXER) += fate-mkv
+FATE_SAMPLES_DEMUX-$(call DEMDEC, MATROSKA, H264) += fate-mkv
 fate-mkv: CMD = framecrc -i $(TARGET_SAMPLES)/mkv/test7_cut.mkv -c copy
 
 FATE_SAMPLES_DEMUX-$(CONFIG_MTV_DEMUXER) += fate-mtv