hw/lan9118.c: Add missing 'break' to fix buffer overrun

Add a missing 'break' statement to fix a buffer overrun when
executing the EEPROM write-all command. Spotted by Coverity
(see bug 887883).
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

hw/lan9118.c

@@ -863,6 +863,7 @@ static void lan9118_eeprom_cmd(lan9118_state *s, int cmd, int addr)
         } else {
             DPRINTF("EEPROM Write All (ignored)\n");
         }
+        break;
     case 5: /* ERASE */
         if (s->eeprom_writable) {
             s->eeprom[addr] = 0xff;