Revert "st/glsl_to_tgsi: don't increase immediate index by 1."

Revert "st/glsl_to_tgsi: don't increase immediate index by 1."

This reverts commit 27d456cc87a01998c6fe1dbf45937e2ca6128495.

DOH, what seems right and what is right with fp64 are always
two different things.

This regressed:
spec@arb_gpu_shader_fp64@shader_storage@layout-std140-fp64-mixed-shader
on radeonsi

Reported-by: Michel Dänzer <michel@daenzer.net>
Cc: "11.2 12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit cb728df9670d8399479db8502145bbc6f653cfb3)