[IA64] Fix Altix BTE error return status

The Altix shub2 BTE error detail bits are in a different location
than on shub1.  The current code does not take this into account
resulting in all shub2 BTE failures mapping to "unknown".

This patch reads the error detail bits from the proper location,
so the correct BTE failure reason is returned for both shub1
and shub2.

Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>