ac3enc: Remove unneeded clipping of shift amount.

s->windowed_samples will always have a range of [-32767,32767] due to the
window function, so the return value from log2_tab() will always be in the
range [0,14].

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 626264b11b)

libavcodec/ac3enc_fixed.c

@@ -309,7 +309,6 @@ static void lshift_tab(int16_t *tab, int n, unsigned int lshift)
 static int normalize_samples(AC3EncodeContext *s)
 {
     int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
-    v = FFMAX(0, v);
     lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
     return v - 9;
 }