make iunique use a do/while loop rather than its obscure goto loop

A while back, Christoph mentioned that he thought that iunique ought to be
cleaned up to use a more conventional loop construct. This patch does that,
turning the strange goto loop into a do/while.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>