glsl: Don't lower_variable_index_to_cond_assign for shared variables

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>

src/glsl/lower_variable_index_to_cond_assign.cpp

@@ -378,6 +378,9 @@ public:
       case ir_var_shader_storage:
 	 return this->lower_uniforms;
 
+      case ir_var_shader_shared:
+	 return false;
+
       case ir_var_function_in:
       case ir_var_const_in:
          return this->lower_temps;