r600: fix r600_buffer_from_user_memory for rusticl

Not entirely sure if it's actually required, but this makes it consistence
with r600_resource_create also calling r600_compute_global_buffer_create
for global memory buffers.

Cc: mesa-stable
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Patrick Lerda <patrick9876@free.fr>

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34623>
1 file changed