iram: in case of double-error, write a correct ecc

hdl/rtl/hydra_iram.vhd

@@ -197,7 +197,7 @@ begin
           else
             --  Uncorrectable.  Just recompute the ECC to be able to continue.
             n_ecc_fatal <= '1';
-            wdata_ecc <= rdata_ecc;
+            wdata_ecc <= recc & rdata_ecc(31 downto 0);
           end if;
           waddr <= last_raddr;
           wen <= '1';