convert fuse_ctl

convert fuse_ctl

objects are created in fuse_ctl_add_dentry() by d_alloc_name()+d_add(),
removed by simple_remove_by_name().

What we return is a borrowed reference - it is valid until the call of
fuse_ctl_remove_conn() and we depend upon the exclusion (on fuse_mutex)
for safety.  Return value is used only within the caller
(fuse_ctl_add_conn()).

Replace d_add() with d_make_persistent() + dput().  dput() is paired
with d_alloc_name() and return value is the result of d_make_persistent().

Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>