cifs: use tcon pointer in cifs_show_options

Minor nit: we already have a tcon pointer so we don't need to
dereference cifs_sb again.

Also initialize the vars in the declaration.

Reported-by: Peter Staubach <staubach@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>