radeonsi: handle first_non_void correctly in si_create_vertex_elements

This fixes R11G11B10_FLOAT, because it's in the category of "OTHER",
meaning that it doesn't have any channel description.

Cc: 17.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
(cherry picked from commit eac7df43ca05abd9992b305e078e88fe7b7f8c91)
1 file changed