Move setting of cxlmd->endpoint to before calling add_device() on the port
device. Otherwise when referencing cxlmd->endpoint in region discovery code
that is triggered by the port driver probe function, the endpoint port
pointer is not valid.

Current code does not hit this issue yet since cxlmd->endpoint is not being
referenced during region discovery. However follow on code that does
performance calculations will.
Tested-by: Wonjae Lee <wj28.lee@samsung.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20240308220055.2172956-9-dave.jiang@intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>