Aufs seems to depend on a positive i_nlink value.  So fill in a dummy but sane
value for the root inode at mount time.

The inode attributes are refreshed with the correct values at the first
opportunity.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>