Linux 3.13 compat: Pass NULL for new delegated inode argument

Note: An old version of SLES (10?) added a 'struct vfsmount *' argument.
That used Linux 2.6.16, which we no longer support. This check was
refactored to support Linux 3.13 without concern for historical versions
of SLES.

Signed-off-by: Richard Yao <ryao@gentoo.org>