fate: increase fuzz on fate-aac-tns-encode test

Fails on SunOS and old GCC (<=4.6 is ancient) versions.

tests/fate/aac.mak

@@ -183,7 +183,7 @@ fate-aac-tns-encode: CMP = stddev
 fate-aac-tns-encode: REF = $(SAMPLES)/audio-reference/luckynight_2ch_44kHz_s16.wav
 fate-aac-tns-encode: CMP_SHIFT = -4096
 fate-aac-tns-encode: CMP_TARGET = 768
-fate-aac-tns-encode: FUZZ = 2.8
+fate-aac-tns-encode: FUZZ = 6
 fate-aac-tns-encode: SIZE_TOLERANCE = 3560
 
 FATE_AAC_ENCODE += fate-aac-is-encode