chore(ggml): migrate submodule to THU-MIG remote

Update the ggml submodule URL to the transferred THU-MIG repository and repoint the gitlink from the pre-transfer commit f97d9273 to its content-identical rewritten commit f270346d. Keep the edge-cudnn-sdpa tracking branch unchanged.

Author: Komorebi623

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "third_party/ggml"]
 	path = third_party/ggml
-	url = https://github.com/Komorebi623/ggml.git
+	url = git@github.com:THU-MIG/ggml.git
 	branch = edge-cudnn-sdpa
 [submodule "third_party/onednn"]
 	path = third_party/onednn