target: remove the unused struct iblock_hba

There is no reason to allocate a struct just to store the host number for
a debug printk in the detach path.  I've simply removed the verbose
debugging given that the calling code thinks the number passed in is
something different from a host ID anyway.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>