avutil/tx_template: Use more unsigned ints to avoid undefined overflows

Fixes: signed integer overflow: 574590586 - -1875616554 cannot be represented in type 'int'
Fixes: 53914/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AAC_FIXED_fuzzer-5037125846564864

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/tx_template.c

@@ -659,7 +659,7 @@ static void TX_NAME(ff_tx_fft8_ns)(AVTXContext *s, void *_dst,
 {
     TXComplex *src = _src;
     TXComplex *dst = _dst;
-    TXSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
+    TXUSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
     const TXSample cos = TX_TAB(ff_tx_tab_8)[1];
 
     TX_NAME(ff_tx_fft4_ns)(s, dst, src, stride);
@@ -680,7 +680,7 @@ static void TX_NAME(ff_tx_fft16_ns)(AVTXContext *s, void *_dst,
     TXComplex *dst = _dst;
     const TXSample *cos = TX_TAB(ff_tx_tab_16);
 
-    TXSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
+    TXUSample t1, t2, t3, t4, t5, t6, r0, i0, r1, i1;
     TXSample cos_16_1 = cos[1];
     TXSample cos_16_2 = cos[2];
     TXSample cos_16_3 = cos[3];