libmix: fix a VC1 parser issue

BZ: 129080

Two issues have been fixed in VC1 parser.
1. User data should be identified.
2. slice_vertical_position should be parsed from bitstream
   instead of being assigned slice number.

Change-Id: I2164550d84720c2619cc2df963d59fc2999faf3a
Signed-off-by: Tianmi Chen <tianmi.chen@intel.com>
1 file changed