avutil/mathematics/av_add_stable: avoid unneeded variable

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/mathematics.c

@@ -188,14 +188,14 @@ simple_round:
 
 int64_t av_add_stable(AVRational ts_tb, int64_t ts, AVRational inc_tb, int64_t inc)
 {
-    AVRational step = av_mul_q(inc_tb, (AVRational) {inc, 1});
+    inc_tb = av_mul_q(inc_tb, (AVRational) {inc, 1});
 
-    if (av_cmp_q(step, ts_tb) < 0) {
+    if (av_cmp_q(inc_tb, ts_tb) < 0) {
         //increase step is too small for even 1 step to be representable
         return ts;
     } else {
-        int64_t old = av_rescale_q(ts, ts_tb, step);
-        int64_t old_ts = av_rescale_q(old, step, ts_tb);
-        return av_rescale_q(old + 1, step, ts_tb) + (ts - old_ts);
+        int64_t old = av_rescale_q(ts, ts_tb, inc_tb);
+        int64_t old_ts = av_rescale_q(old, inc_tb, ts_tb);
+        return av_rescale_q(old + 1, inc_tb, ts_tb) + (ts - old_ts);
     }
 }