Fixed broken call to my_error

sql/sql_yacc.yy:
  Fixed error message to use char*, not LEX_STRING

sql/sql_yacc.yy

@@ -5087,7 +5087,7 @@ simple_expr:
                   the case when a default database exist, see below.
                 */
                 my_error(ER_SP_DOES_NOT_EXIST, MYF(0),
-                         "FUNCTION", $1);
+                         "FUNCTION", $1.str);
                 MYSQL_YYABORT;
               }