[SCSI] ipr: Fix target id allocation re-use problem

For the latest ipr SAS adapters, target id's are a completely
logical construct that are managed in the ipr driver. This fixes
an issue that can arise if a device is deleted via sysfs. If
a new device is then physically added, it will use the previous
device's target id. If the host is then rescanned, the device
that had been deleted, since it is using the same target id as
the new device is using, will never be found, resulting in
a missing device. Fix this by only freeing the target id
only if the resource is actually gone.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>