[PATCH] ocfs2: fix thinko in ocfs2_backup_super_blkno()

Fix a bug which was introduced when I synced up ocfs2_fs.h with ocfs2-tools.
We can't do u64/u32 in kernel.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>