fuse_ctl_add_conn(): fix nlink breakage in case of early failure

fuse_ctl_add_conn(): fix nlink breakage in case of early failure

fuse_ctl_remove_conn() used to decrement the link count of root
manually; that got subsumed by simple_recursive_removal(), but
in case when subdirectory creation has failed the latter won't
get called.

Just move the modification of parent's link count into
fuse_ctl_add_dentry() to keep the things simple.  Allows to
get rid of the nlink argument as well...

Fixes: fcaac5b42768 "fuse_ctl: use simple_recursive_removal()"
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>