btrfs: Fix calculation of rbio->dbitmap's size calculation

Current code is trying to calculate rbio->dbitmap's size to make it
align to sizeof(long), but implement haven't achived this object,
it is align to sizeof(char) instead.
This patch fixed above calculation, and use sizeof(long) instead of
fixed "8" to increate compatibility.
Signed-off-by: NZhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/raid56.c

@@ -966,8 +966,8 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_root *root,
 	void *p;
 
 	rbio = kzalloc(sizeof(*rbio) + num_pages * sizeof(struct page *) * 2 +
-		       DIV_ROUND_UP(stripe_npages, BITS_PER_LONG / 8),
-			GFP_NOFS);
+		       DIV_ROUND_UP(stripe_npages, BITS_PER_LONG) *
+		       sizeof(long), GFP_NOFS);
 	if (!rbio)
 		return ERR_PTR(-ENOMEM);
 

fs/btrfs/scrub.c

@@ -2813,7 +2813,7 @@ static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
 
 static inline int scrub_calc_parity_bitmap_len(int nsectors)
 {
-	return DIV_ROUND_UP(nsectors, BITS_PER_LONG) * (BITS_PER_LONG / 8);
+	return DIV_ROUND_UP(nsectors, BITS_PER_LONG) * sizeof(long);
 }
 
 static void scrub_parity_get(struct scrub_parity *sparity)