md: support bitmaps on RAID10 arrays larger then 2 terabytes

.. and other arrays with components larger than 2 terabytes.

We use a "long" rather than a "sector_t" in part of the bitmap
size calculations, which is sad.
Reported-by: "Mario 'BitKoenig' Holbe" <Mario.Holbe@TU-Ilmenau.DE>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/bitmap.c

@@ -1590,7 +1590,7 @@ void bitmap_destroy(mddev_t *mddev)
 int bitmap_create(mddev_t *mddev)
 {
 	struct bitmap *bitmap;
-	unsigned long blocks = mddev->resync_max_sectors;
+	sector_t blocks = mddev->resync_max_sectors;
 	unsigned long chunks;
 	unsigned long pages;
 	struct file *file = mddev->bitmap_file;
@@ -1632,8 +1632,8 @@ int bitmap_create(mddev_t *mddev)
 	bitmap->chunkshift = ffz(~bitmap->chunksize);
 
 	/* now that chunksize and chunkshift are set, we can use these macros */
- 	chunks = (blocks + CHUNK_BLOCK_RATIO(bitmap) - 1) /
-			CHUNK_BLOCK_RATIO(bitmap);
+ 	chunks = (blocks + CHUNK_BLOCK_RATIO(bitmap) - 1) >>
+			CHUNK_BLOCK_SHIFT(bitmap);
  	pages = (chunks + PAGE_COUNTER_RATIO - 1) / PAGE_COUNTER_RATIO;
 
 	BUG_ON(!pages);