fate/api: add missing FLV dependency to fate-api-seek

tests/fate/api.mak

@@ -14,7 +14,7 @@ FATE_API_SAMPLES_LIBAVFORMAT-$(call DEMDEC, H264, H264) += fate-api-h264
 fate-api-h264: $(APITESTSDIR)/api-h264-test$(EXESUF)
 fate-api-h264: CMD = run $(APITESTSDIR)/api-h264-test $(TARGET_SAMPLES)/h264-conformance/SVA_NL2_E.264
 
-FATE_API_LIBAVFORMAT-yes += fate-api-seek
+FATE_API_LIBAVFORMAT-$(call DEMDEC, FLV, FLV) += fate-api-seek
 fate-api-seek: $(APITESTSDIR)/api-seek-test$(EXESUF) fate-lavf
 fate-api-seek: CMD = run $(APITESTSDIR)/api-seek-test $(TARGET_PATH)/tests/data/lavf/lavf.flv 0 720
 fate-api-seek: CMP = null