msdkdec: postpone surface free for VC1
For a skipped frame in VC1, MSDK returns the mfx surface of the reference frame, so we have to make sure the corresponding surface for the reference frame is not freed. In this fix, we postpone surface free because we don't know whether a surface is referenced
Before this fix, the error is like as below:
New clock: GstSystemClock 0:00:00.181793130 23098 0x55f8a9d622d0 ERROR msdkdec gstmsdkdec.c:622:gst_msdkdec_finish_task: Couldn't find the cached MSDK surface
Sample pipeline: gst-launch-1.0 filesrc location=input_has_skipped_frame.wmv ! asfdemux ! vc1parse ! msdkvc1dec ! glimagesink