omxvideodec: Use GST_VIDEO_FRAME_PLANE_STRIDE() to get output buffer's stride

GST_VIDEO_FRAME_PLANE_STRIDE() should be used to get the actual buffer stride,
as reported in the buffers's GstVideoMeta, when copying data to that buffer.

https://bugzilla.gnome.org/show_bug.cgi?id=768173

omx/gstomxvideodec.c

@@ -515,7 +515,7 @@ gst_omx_video_dec_fill_buffer (GstOMXVideoDec * self,
       data = src;
       for (h = 0; h < dst_height[p]; h++) {
         memcpy (dst, data, dst_width[p]);
-        dst += GST_VIDEO_INFO_PLANE_STRIDE (vinfo, p);
+        dst += GST_VIDEO_FRAME_PLANE_STRIDE (&frame, p);
         data += src_stride[p];
       }
       src += src_size[p];