cxl/mem: Clarify @host for devm_cxl_add_nvdimm()

cxl/mem: Clarify @host for devm_cxl_add_nvdimm()

The convention for devm_ helpers in the CXL driver is that the first
argument is the @host for the operation (locked driver::probe() context).

Reviewed-by: Terry Bowman <terry.bowman@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20260114182055.46029-17-terry.bowman@amd.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>