lavu: define FF_MEMORY_POISON and use it

Allow single-place definition of constant used to fill poisoned memory.

libavutil/buffer.c

@@ -288,7 +288,7 @@ static void pool_release_buffer(void *opaque, uint8_t *data)
     AVBufferPool *pool = buf->pool;
 
     if(CONFIG_MEMORY_POISONING)
-        memset(buf->data, 0x2a, pool->size);
+        memset(buf->data, FF_MEMORY_POISON, pool->size);
 
     add_to_pool(buf);
     if (!avpriv_atomic_int_add_and_fetch(&pool->refcount, -1))

libavutil/internal.h

@@ -66,6 +66,8 @@
 #    define INT_BIT (CHAR_BIT * sizeof(int))
 #endif
 
+#define FF_MEMORY_POISON 0x2a
+
 // Some broken preprocessors need a second expansion
 // to be forced to tokenize __VA_ARGS__
 #define E1(x) x

libavutil/mem.c

@@ -133,7 +133,7 @@ void *av_malloc(size_t size)
     }
 #if CONFIG_MEMORY_POISONING
     if (ptr)
-        memset(ptr, 0x2a, size);
+        memset(ptr, FF_MEMORY_POISON, size);
 #endif
     return ptr;
 }