cxl: Refactor to use __free() for cxl_root allocation in cxl_endpoint_port_probe()

Use scope-based resource management __free() macro to drop the open coded
put_device() in cxl_endpoint_port_probe().

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/170449247973.3779673.15088722836135359275.stgit@djiang5-mobl3


Signed-off-by: Dan Williams <dan.j.williams@intel.com>