cxl/memdev: Pin parents for entire memdev lifetime

cxl/memdev: Pin parents for entire memdev lifetime

In order to be able to manage the driver that uses a memdev attach
mechanism the parent needs to stick around for the
device_release_driver(cxlmd->dev.parent) event.

Fixes: 29317f8dc6ed ("cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation")
Signed-off-by: Dan Williams <djbw@kernel.org>
Reviewed-by: Alejandro Lucero <alucerop@amd.com>
Tested-by: ALejandro Lucero <alucerop@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/20260519210158.1499795-4-djbw@kernel.org
Signed-off-by: Dave Jiang <dave.jiang@intel.com>