cxl: Set range param for region_res_match_cxl_range() as const

The function takes two parameters and compares them. The second parameter
should be const since no modification should be done to it.

Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>