avcodec/cbs_av1: Avoid shift overflow

Fixes: CID1465488 Unintentional integer overflow

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cbs_av1.c

@@ -301,7 +301,7 @@ static int cbs_av1_write_increment(CodedBitstreamContext *ctx, PutBitContext *pb
         return AVERROR(ENOSPC);
 
     if (len > 0)
-        put_bits(pbc, len, (1 << len) - 1 - (value != range_max));
+        put_bits(pbc, len, (1U << len) - 1 - (value != range_max));
 
     CBS_TRACE_WRITE_END_NO_SUBSCRIPTS();