mm: remove reference to PG_buddy

PG_buddy doesn't exist any more.  It's called PageBuddy now.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Cc: Randy Dunlap <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Matthew Wilcox

include/linux/mm_types.h

@@ -175,13 +175,13 @@ struct page {
 	};
 
 	union {
-		unsigned long private;		/* Mapping-private opaque data:
-					 	 * usually used for buffer_heads
-						 * if PagePrivate set; used for
-						 * swp_entry_t if PageSwapCache;
-						 * indicates order in the buddy
-						 * system if PG_buddy is set.
-						 */
+		/*
+		 * Mapping-private opaque data:
+		 * Usually used for buffer_heads if PagePrivate
+		 * Used for swp_entry_t if PageSwapCache
+		 * Indicates order in the buddy system if PageBuddy
+		 */
+		unsigned long private;
 #if USE_SPLIT_PTE_PTLOCKS
 #if ALLOC_SPLIT_PTLOCKS
 		spinlock_t *ptl;