avcodec/vorbis: 1 << 31 > int32_t::max(), so use 1u << 31 instead.

Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9648cc6d7f)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/vorbis.c

@@ -105,7 +105,7 @@ int ff_vorbis_len2vlc(uint8_t *bits, uint32_t *codes, unsigned num)
         exit_at_level[i] = 0;
         // construct code (append 0s to end) and introduce new exits
         for (j = i + 1 ;j <= bits[p]; ++j)
-            exit_at_level[j] = code + (1 << (j - 1));
+            exit_at_level[j] = code + (1u << (j - 1));
         codes[p] = code;
 
 #ifdef DEBUG