st/mesa: Switch glsl_to_tgsi_instruction to the non-zeroing allocator.

All member variables of glsl_to_tgsi_instruction are already being
initialized from its implicitly defined constructor, it's not
necessary to use rzalloc to allocate its memory.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -217,7 +217,7 @@ st_dst_reg::st_dst_reg(st_src_reg reg)
 
 class glsl_to_tgsi_instruction : public exec_node {
 public:
-   DECLARE_RZALLOC_CXX_OPERATORS(glsl_to_tgsi_instruction)
+   DECLARE_RALLOC_CXX_OPERATORS(glsl_to_tgsi_instruction)
 
    unsigned op;
    st_dst_reg dst;