aacenc_utils: Use temporary variable.

This ensures gcc does not create unnecessary
loads or stores and possibly even does not vectorize
the negation.
Speeds up mp3 to aac transcoding with default settings
by 10% when using "gcc (Debian 5.3.1-10) 5.3.1 20160224".

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/aacenc_utils.h

@@ -68,10 +68,11 @@ static inline void quantize_bands(int *out, const float *in, const float *scaled
     int i;
     for (i = 0; i < size; i++) {
         float qc = scaled[i] * Q34;
-        out[i] = (int)FFMIN(qc + rounding, (float)maxval);
+        int tmp = (int)FFMIN(qc + rounding, (float)maxval);
         if (is_signed && in[i] < 0.0f) {
-            out[i] = -out[i];
+            tmp = -tmp;
         }
+        out[i] = tmp;
     }
 }