radv: fix emitting the TCS regs on GFX9

The primitive ID is NULL and this generates an invalid
select instruction which crashes because one operand is NULL.

This fixes crashes in The Long Journey Home, Quantum Break
and Just Cause 3 with DXVK.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106756


CC: <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 5917761e)