radv/gfx10: fix storing/loading NGG stream outputs for VS and TES

radv/gfx10: fix storing/loading NGG stream outputs for VS and TES

The LDS storage allocated for stream outputs is 4 * N, where N
is the number of outputs. So, we have to store/load with N as index
and not with the output location as index.

This doesn't fix anything known but it should fix out-of-bounds
access and it also reduces the number of outputs written to the
LDS storage.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>