radv: handle loc->indirect correctly for the first descriptor

This was wrong for descriptor #0 when all of them are indirect.
This is because indirect_offset was 0 and we emitted a
"normal" descriptor pointer for nothing.

While we are at it remove
radv_userdata_info::indirect_offset which is useless.

CC: 18.2 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit aa302059)