[PATCH] cleanups and bug fix in do_loopback()

 - check_mnt() on the source of binding should've been unconditional
   from the very beginning.  My fault - as far I could've trace it,
   that's an old thinko made back in 2001.  Kudos to Miklos for spotting
   it...

   Fixed.

 - code cleaned up.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>