Update Vulkan RoPE implementation (#7818)

* Update Vulkan RoPE implementation

* Return nullptr on alloc_buffer when allocation fails, instead of throwing an exception

Minor fixes

* Fix segfault when running out of VRAM

Co-authored-by: slaren <slarengh@gmail.com>

---------

Co-authored-by: slaren <slarengh@gmail.com>

ggml-alloc.c

@@ -886,7 +886,7 @@ static bool alloc_tensor_range(struct ggml_context * ctx,
         fprintf(stderr, "%s: failed to allocate %s buffer of size %zu\n", __func__, ggml_backend_buft_name(buft), size);
 #endif
         for (size_t i = 0; i < *n_buffers; i++) {
-            ggml_backend_buffer_free(*buffers[i]);
+            ggml_backend_buffer_free((*buffers)[i]);
         }
         free(*buffers);
         return false;