glsl: Fix segfault due to missing printf argument

Fixes the following Piglit tests:
glslparsertest/shaders/array2.frag
glslparsertest/shaders/dataType6.frag

NOTE: This is a candidate for the 7.9 and 7.10 branches.

src/glsl/ast_to_hir.cpp

@@ -2509,7 +2509,8 @@ ast_declarator_list::hir(exec_list *instructions,
        */
       if (this->type->qualifier.flags.q.constant && decl->initializer == NULL) {
 	 _mesa_glsl_error(& loc, state,
-			  "const declaration of `%s' must be initialized");
+			  "const declaration of `%s' must be initialized",
+			  decl->identifier);
       }
 
       /* Check if this declaration is actually a re-declaration, either to