fuse: Linking file to inode helper

When writeback is ON every writeable file should be in per-inode write list,
not only mmap-ed ones. Thus introduce a helper for this linkage.

Change-Id: I9c4df97354b8f7c14de1106ccad24a3fb78319c4
Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Git-commit:  650b22b941fa03590c4a3671e79ec2c96ea59e9a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git


Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>