avutil/buffer: use the old atomics based code for the release branch

the old code worked fine for a long time and was not affected by
the bug the new code fixes and the new is not widely tested yet.
This can be reverted once the code received more testing in
master

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

libavutil/buffer.c

@@ -25,7 +25,8 @@
 #include "mem.h"
 #include "thread.h"
 
-#define USE_ATOMICS !(HAVE_PTHREADS || HAVE_W32THREADS)
+//#define USE_ATOMICS !(HAVE_PTHREADS || HAVE_W32THREADS)
+#define USE_ATOMICS 1 // can be changed to the above once it received more testing in master
 
 AVBufferRef *av_buffer_create(uint8_t *data, int size,
                               void (*free)(void *opaque, uint8_t *data),