cxl/port: Keep port->uport valid for the entire life of a port

The upcoming region provisioning implementation has a need to
dereference port->uport during the port unregister flow. Specifically,
endpoint decoders need to be able to lookup their corresponding memdev
via port->uport.

The existing ->dead flag was added for cases where the core was
committed to tearing down the port, but needed to drop locks before
calling device_unregister(). Reuse that flag to indicate to
delete_endpoint() that it has no "release action" work to do as
unregister_port() will handle it.
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Adam Manzanares <a.manzanares@samsung.com>
Link: https://lore.kernel.org/r/165603871491.551046.6682199179541194356.stgit@dwillia2-xfhSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/port.c

@@ -370,7 +370,7 @@ static void unregister_port(void *_port)
 		lock_dev = &parent->dev;
 
 	device_lock_assert(lock_dev);
-	port->uport = NULL;
+	port->dead = true;
 	device_unregister(&port->dev);
 }
 
@@ -857,7 +857,7 @@ static void delete_endpoint(void *data)
 	parent = &parent_port->dev;
 
 	device_lock(parent);
-	if (parent->driver && endpoint->uport) {
+	if (parent->driver && !endpoint->dead) {
 		devm_release_action(parent, cxl_unlink_uport, endpoint);
 		devm_release_action(parent, unregister_port, endpoint);
 	}