fate/pixlet: Fix test requirements

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

tests/fate/pixlet.mak

-FATE_PIXLET += fate-pixlet-rgb
+FATE_PIXLET-$(call FRAMECRC, MOV, PIXLET, SCALE_FILTER) += fate-pixlet-rgb
 fate-pixlet-rgb: CMD = framecrc -i $(TARGET_SAMPLES)/pixlet/pixlet_rgb.mov -an -pix_fmt yuv420p16le -vf scale
 
-FATE_SAMPLES_AVCONV-$(call DEMDEC, MOV, PIXLET) += $(FATE_PIXLET)
-fate-pixlet: $(FATE_PIXLET)
+FATE_SAMPLES_FFMPEG += $(FATE_PIXLET-yes)
+fate-pixlet: $(FATE_PIXLET-yes)