cxl/trace: Subtract to find an hpa_alias0 in cxl_poison events

Traces of cxl_poison events include an hpa_alias0 field if the poison
address is in a region configured with an ELC, Extended Linear Cache.

Since the ELC always comes first in the region, the calculation needs
to subtract the ELC size from the calculated HPA address.

Fixes: 8c520c5f ("cxl: Add extended linear cache address alias emission for cxl events")
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>