pipewire: impl-core: actually return created object

Actually return the pointer to the created object
from `impl-core.c:core_create_object()` instead of
returning a NULL pointer.

This has not caused issues because the return value
is not checked anywhere.

src/pipewire/impl-core.c

@@ -351,7 +351,7 @@ core_create_object(void *object,
 	if (obj == NULL)
 		goto error_create_failed;
 
-	return 0;
+	return obj;
 
 error_no_factory:
 	res = -ENOENT;