ac/nir: fix getting GLSL type of array of samplers for TG4

This fixes a crash in build_tex_intrinsic() when trying to
launch the Basemark GPU benchmark on GFX8. It looks like
there is still something wrong because some frames are black.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106980


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 4c43ec46)