util/prim_restart: fix util_translate_prim_restart_ib

util/prim_restart: fix util_translate_prim_restart_ib

this was broken for the indirect case if the indirect draw count or
firstIndex was nonzero and also would rewrite the index buffer onto the
wrong offset of the dst buffer

Fixes: 0c85d6c523f ("gallium/util: factor out primitive-restart rewriting logic")
Fixes: 330d0607ed6 ("gallium: remove pipe_index_buffer and set_index_buffer")

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10909>