ggml : add asserts for type conversion in fattn kernels (#9971)

ggml-ci

src/llama.cpp

@@ -19243,7 +19243,7 @@ struct llama_context * llama_new_context_with_model(
         params.flash_attn = false;
     }
 
-    if (params.type_v != GGML_TYPE_F16 && !params.flash_attn) {
+    if (ggml_is_quantized(params.type_v) && !params.flash_attn) {
         LLAMA_LOG_ERROR("%s: V cache quantization requires flash_attn\n", __func__);
         return nullptr;
     }