nvc0: return NULL instead of asserting in nvc0_resource_from_user_memory

Fixes: 212f1ab40e ("nvc0: support PIPE_CAP_RESOURCE_FROM_USER_MEMORY_COMPUTE_ONLY")
Acked-by: David Heidelberg <david@ixit.cz>
Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27783>

src/gallium/drivers/nouveau/nvc0/nvc0_resource.c

@@ -141,11 +141,9 @@ nvc0_resource_from_user_memory(struct pipe_screen *pipe,
                                const struct pipe_resource *templ,
                                void *user_memory)
 {
-   ASSERTED struct nouveau_screen *screen = nouveau_screen(pipe);
-
-   assert(screen->has_svm);
-   assert(templ->target == PIPE_BUFFER);
-
+   struct nouveau_screen *screen = nouveau_screen(pipe);
+   if (!screen->has_svm || templ->target != PIPE_BUFFER)
+      return NULL;
    return nouveau_buffer_create_from_user(pipe, templ, user_memory);
 }