bitstream_reader: Try to fix "get_bits.h:305:45: warning: variable ‘re_cache’...

bitstream_reader: Try to fix "get_bits.h:305:45: warning: variable ‘re_cache’ set but not used [-Wunused-but-set-variable]"
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/get_bits.h

@@ -127,7 +127,7 @@ for examples see get_bits, show_bits, skip_bits, get_vlc
 
 #   define OPEN_READER(name, gb)                \
     unsigned int name##_index = (gb)->index;    \
-    int name##_cache
+    av_unused int name##_cache
 
 #   define CLOSE_READER(name, gb) (gb)->index = name##_index