cxl/region: Simplify cxl_region_nid()

The node ID of the region can be gotten via resource start address
directly.  This simplifies the implementation of cxl_region_nid().

Signed-off-by: Huang Ying <ying.huang@intel.com>
Suggested-by: Alison Schofield <alison.schofield@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/20240618084639.1419629-4-ying.huang@intel.com


Signed-off-by: Dave Jiang <dave.jiang@intel.com>