bootmem: replace node_boot_start in struct bootmem_data

Almost all users of this field need a PFN instead of a physical address,
so replace node_boot_start with node_min_pfn.

[Lee.Schermerhorn@hp.com: fix spurious BUG_ON() in mark_bootmem()]
Signed-off-by: Johannes Weiner <hannes@saeureba.de>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/m32r/mm/discontig.c b/arch/m32r/mm/discontig.c
index cc23934..cbc3c4c 100644
--- a/arch/m32r/mm/discontig.c
+++ b/arch/m32r/mm/discontig.c
@@ -123,8 +123,7 @@
 	return max_low_pfn;
 }
 
-#define START_PFN(nid)	\
-	(NODE_DATA(nid)->bdata->node_boot_start >> PAGE_SHIFT)
+#define START_PFN(nid)		(NODE_DATA(nid)->bdata->node_min_pfn)
 #define MAX_LOW_PFN(nid)	(NODE_DATA(nid)->bdata->node_low_pfn)
 
 unsigned long __init zone_sizes_init(void)