Fix the issue of on x86_64, rhel4 can not get into runlevel 5.

diff -r dc250958aebb -r 43babde5b509 tools/ioemu/exec.c
@@ -262,6 +262,15 @@
                                   unsigned long size,
                                   unsigned long phys_offset)
 {
+        int i;
+
+        for (i = 0; i < mmio_cnt; i++) { 
+            if(mmio[i].start == start_addr) {
+                mmio[i].io_index = phys_offset;
+                mmio[i].size = size;
+                return;
+            }
+        }
         if (mmio_cnt == MAX_MMIO) {
                 fprintf(logfile, "too many mmio regions\n");
                 exit(-1);