svga: fix draw elements with 8-bits indices

svga: fix draw elements with 8-bits indices

With commit 2122b902b80, u_index_translator can return U_TRANSLATE_MEMCPY
for 8-bits indices, and in this case we need to call the translation function
instead of a simple passthrough to the device.

Fixes piglit spec@nv_primitive_restart tests.

Fixes: 2122b902b8 "gallium/indices: don't expand prim-type for 8-bit indices"
Reviewed-by: Neha Bhende <bhenden@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6414>