rangecoder: fix "incompatible pointer type" warning

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

libavcodec/rangecoder.c

@@ -54,7 +54,7 @@ void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size){
     /* cast to avoid compiler warning */
     ff_init_range_encoder(c, (uint8_t *) buf, buf_size);
 
-    c->low = bytestream_get_be16(&c->bytestream);
+    c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
 }
 
 void ff_build_rac_states(RangeCoder *c, int factor, int max_p){