glsl_to_tgsi: Fix typo shader_program -> shader

This was a regression introduced by commit
f4b0ab7afd ('st/mesa: fix incorrect size
of UBO declarations') which caused an assertion failure while compiling
shaders of e.g. UE4 demos.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81834
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -5113,8 +5113,7 @@ st_translate_program(
       unsigned num_ubos = program->shader->NumUniformBlocks;
 
       for (i = 0; i < num_ubos; i++) {
-         unsigned size =
-            program->shader_program->UniformBlocks[i].UniformBufferSize;
+         unsigned size = program->shader->UniformBlocks[i].UniformBufferSize;
          unsigned num_const_vecs = (size + 15) / 16;
          unsigned first, last;
          assert(num_const_vecs > 0);