intel/aubinator: Trust the packet size in the header for SUBOPCODE_HEADER

intel/aubinator: Trust the packet size in the header for SUBOPCODE_HEADER

We were reading from the "comment size" dword and incrementing by that
amount.  This never caused a problem because that field was always zero.
However, experimenting with actual aub file comments indicates, the
simulator seems to include the comment size in the packet size provided in
the header.  We should do the same.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>