cxl/region: Rename misleading variable name @hpa to @hpa_range

cxl/region: Rename misleading variable name @hpa to @hpa_range

@hpa is actually a @hpa_range, rename variables accordingly.

Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Robert Richter <rrichter@amd.com>
Link: https://patch.msgid.link/20260114164837.1076338-2-rrichter@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>