mm: fix fatal kernel-doc error

Fix a fatal kernel-doc error due to a #define coming between a function's
kernel-doc notation and the function signature.  (kernel-doc cannot handle
this)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page-writeback.c

@@ -825,10 +825,10 @@ void __init page_writeback_init(void)
 /*
  * We tag pages in batches of WRITEBACK_TAG_BATCH to reduce tree_lock latency.
  */
-#define WRITEBACK_TAG_BATCH 4096
 void tag_pages_for_writeback(struct address_space *mapping,
 			     pgoff_t start, pgoff_t end)
 {
+#define WRITEBACK_TAG_BATCH 4096
 	unsigned long tagged;
 
 	do {