One small fix for md/bitmaps

This fixes a regression that was introduced in the merge window.
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Merge tag 'md-3.4-fixes' of git://neil.brown.name/md

Pull one small fix for md/bitmaps from NeilBrown:
 "This fixes a regression that was introduced in the merge window."

* tag 'md-3.4-fixes' of git://neil.brown.name/md:
  md/bitmap: fix calculation of 'chunks' - missing shift.

drivers/md/bitmap.c

@@ -1727,8 +1727,7 @@ int bitmap_create(struct mddev *mddev)
 	bitmap->chunkshift = (ffz(~mddev->bitmap_info.chunksize)
 			      - BITMAP_BLOCK_SHIFT);
 
-	/* now that chunksize and chunkshift are set, we can use these macros */
-	chunks = (blocks + bitmap->chunkshift - 1) >>
+	chunks = (blocks + (1 << bitmap->chunkshift) - 1) >>
 			bitmap->chunkshift;
 	pages = (chunks + PAGE_COUNTER_RATIO - 1) / PAGE_COUNTER_RATIO;
 

drivers/md/bitmap.h

@@ -101,9 +101,6 @@ typedef __u16 bitmap_counter_t;
 
 #define BITMAP_BLOCK_SHIFT 9
 
-/* how many blocks per chunk? (this is variable) */
-#define CHUNK_BLOCK_RATIO(bitmap) ((bitmap)->mddev->bitmap_info.chunksize >> BITMAP_BLOCK_SHIFT)
-
 #endif
 
 /*