ra144enc: avoid integer overflows.

The values are all positive but signed variables where used,
which overflowed.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/ra144enc.c

@@ -347,7 +347,8 @@ static void ra144_encode_subblock(RA144Context *ractx,
     float zero[BLOCKSIZE], cba[BLOCKSIZE], cb1[BLOCKSIZE], cb2[BLOCKSIZE];
     int16_t cba_vect[BLOCKSIZE];
     int cba_idx, cb1_idx, cb2_idx, gain;
-    int i, n, m[3];
+    int i, n;
+    unsigned m[3];
     float g[3];
     float error, best_error;