mm/memory_hotplug.c: use PFN_DOWN()

Replace ((x) >> PAGE_SHIFT) with the pfn macro.
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -1069,7 +1069,7 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 	struct pglist_data *pgdat;
 	unsigned long zones_size[MAX_NR_ZONES] = {0};
 	unsigned long zholes_size[MAX_NR_ZONES] = {0};
-	unsigned long start_pfn = start >> PAGE_SHIFT;
+	unsigned long start_pfn = PFN_DOWN(start);
 
 	pgdat = NODE_DATA(nid);
 	if (!pgdat) {
@@ -1141,7 +1141,7 @@ int try_online_node(int nid)
 
 static int check_hotplug_memory_range(u64 start, u64 size)
 {
-	u64 start_pfn = start >> PAGE_SHIFT;
+	u64 start_pfn = PFN_DOWN(start);
 	u64 nr_pages = size >> PAGE_SHIFT;
 
 	/* Memory range must be aligned with section */