mmal/codec: Clear data from buffer header before release

The data attached to the output port headers is not owned by the codec but by
the vout and only temporarily attached to the codecs buffers. To avoid
refcount issues within the mmal core clear the data field before releasing the
buffers.
Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/hw/mmal/codec.c

@@ -460,6 +460,7 @@ static int send_output_buffer(decoder_t *dec)
 err:
     if (picture)
         picture_Release(picture);
+    buffer->data = NULL;
     mmal_buffer_header_release(buffer);
     return ret;
 }
@@ -549,6 +550,7 @@ static picture_t *decode(decoder_t *dec, block_t **pblock)
             ret->b_progressive = sys->b_progressive;
             ret->b_top_field_first = sys->b_top_field_first;
 
+            buffer->data = NULL;
             mmal_buffer_header_reset(buffer);
             mmal_buffer_header_release(buffer);
         }