fate/screen: workaround test failure on mac M1

The last frame is corrupted. It has different results on different
platform.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>

tests/fate/screen.mak

@@ -117,7 +117,8 @@ FATE_SCREEN += $(FATE_VMNC-yes)
 fate-vmnc: $(FATE_VMNC-yes)
 
 FATE_ZMBV += fate-zmbv-8bit
-fate-zmbv-8bit: CMD = framecrc -i $(TARGET_SAMPLES)/zmbv/wc2_001-partial.avi -an -pix_fmt rgb24 -vf scale
+# The last frame is corrupted.
+fate-zmbv-8bit: CMD = framecrc -i $(TARGET_SAMPLES)/zmbv/wc2_001-partial.avi -an -frames:v 275 -pix_fmt rgb24 -vf scale
 
 FATE_ZMBV += fate-zmbv-15bit
 fate-zmbv-15bit: CMD = framecrc -i $(TARGET_SAMPLES)/zmbv/zmbv_15bit.avi -pix_fmt rgb24 -t 25 -vf scale

tests/ref/fate/zmbv-8bit

@@ -278,4 +278,3 @@
 0,        272,        272,        1,   192000, 0xd08e49d1
 0,        273,        273,        1,   192000, 0xd08e49d1
 0,        274,        274,        1,   192000, 0xd08e49d1
-0,        275,        275,        1,   192000, 0x1f34135f