Don't ignore the return value of create_tensors()

else, when q, k, v get merged and we are running on the CPU,
we get a crash because the backend is trying to use mmap,
but that no longer works.

src/llama.cpp

@@ -1684,7 +1684,7 @@ static bool llm_load_tensors(
         throw std::runtime_error("model has expert layers but no expert layers are used");
     }
 
-    cth->create_tensors();
+    use_mmap_buffer = cth->create_tensors();
 
     ml.done_getting_tensors();