md: fix several trivial typos in comments

Signed-off-by: Zhilong Liu <zlliu@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index cc7bbd2..bf7419a 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -697,7 +697,7 @@ static int bitmap_read_sb(struct bitmap *bitmap)
 
 out:
 	kunmap_atomic(sb);
-	/* Assiging chunksize is required for "re_read" */
+	/* Assigning chunksize is required for "re_read" */
 	bitmap->mddev->bitmap_info.chunksize = chunksize;
 	if (err == 0 && nodes && (bitmap->cluster_slot < 0)) {
 		err = md_setup_cluster(bitmap->mddev, nodes);