.gitmodules: fix incorrect llvm repo url

Fixes: e3082e2 ("gitsubmodules: update llvm-rust submodule branch")
Signed-off-by: Jinghao Jia <[email protected]>

Author: jinghao-jia

Diff for: .gitmodules

@@ -32,7 +32,7 @@
 	shallow = true
 [submodule "src/llvm-project"]
 	path = src/llvm-project
-	url = https://github.com/xlab-uiuc/rust.git
+	url = https://github.com/xlab-uiuc/llvm-rust.git
 	branch = rex-llvm
 [submodule "src/doc/embedded-book"]
 	path = src/doc/embedded-book