ufs: convert ufs to the new mount API

Convert ufs to the new mount API

Removed a BUG_ON from show_options(); worst case, it prints
a null string where the BUG_ON would have fired.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>