linux-ramdump-parser-v2: Correct pfn_to_page with a pfn offset

When calculating pfn_to_page, the pfn needs to be offset before
indexing into the array. Account for this.

Change-Id: If207447a91537ab7670058fede65473d3ea93281

linux-ramdump-parser-v2/mm.py

@@ -135,7 +135,7 @@ def pfn_to_page_flat(ramdump, pfn):
     page_size = ramdump.sizeof('struct page')
     # XXX Needs to change for LPAE
     pfn_offset = ramdump.phys_offset >> 12
-    return mem_map + (pfn * page_size) - pfn_offset
+    return mem_map + ((pfn - pfn_offset) * page_size)
 
 
 def page_to_pfn(ramdump, page):