ttn: Fix out-of-bounds accesses since the always-2D-constants change.

ttn: Fix out-of-bounds accesses since the always-2D-constants change.

Only one of the three checks for dim was updated, so we would try to set a
UBO buffer index source value on a nir_load_uniform, and wouldn't actually
declare non-UBO uniforms.

Fixes: 37dd8e8dee1d ("gallium: all drivers should accept two-dimensional constant buffer indexing")
Tested-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>