libavcodec/amfenc_h264.c: Changed loop filter flag default value.

The value has been changed to match the recommended(by AMF Encoder team)

libavcodec/amfenc_h264.c

@@ -366,6 +366,7 @@ static const AVCodecDefault defaults[] = {
     { "b",          "2M"  },
     { "g",          "250" },
     { "slices",     "1"   },
+    { "flags",      "+loop"},
     { NULL                },
 };