Fix name error in migration stream analyzation script

It fixes the following error:

Traceback (most recent call last):
  File "./scripts/analyze-migration.py", line 584, in <module>
    dump.read(dump_memory = args.memory)
  File "./scripts/analyze-migration.py", line 528, in read
    self.sections[section_id].read()
  File "./scripts/analyze-migration.py", line 250, in read
    self.file.readvar(n_valid * HASH_PTE_SIZE_64)
NameError: global name 'HASH_PTE_SIZE_64' is not defined

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

scripts/analyze-migration.py

@@ -247,7 +247,7 @@ def read(self):
             if index == 0 and n_valid == 0 and n_invalid == 0:
                 break
 
-            self.file.readvar(n_valid * HASH_PTE_SIZE_64)
+            self.file.readvar(n_valid * self.HASH_PTE_SIZE_64)
 
     def getDict(self):
         return ""