avcodec/aacdec_usac: Fix array size

The array in ff_aac_usac_mdst_filt_cur that is passed to that has a size
of 7 elements, not 6 and the code in the function accesses the array at
index 6, which would be out of bounds if the size was actually 6.

Fixes: CID1603196

libavcodec/aac/aacdec_usac.c

@@ -1134,7 +1134,7 @@ static void complex_stereo_downmix_cur(AACDecContext *ac, ChannelElement *cpe,
     }
 }
 
-static void complex_stereo_interpolate_imag(float *im, float *re, const float f[6],
+static void complex_stereo_interpolate_imag(float *im, float *re, const float f[7],
                                             int len, int factor_even, int factor_odd)
 {
     int i = 0;