[SCSI] fc class: fix scanning when devs are offline

When a rport is added back or the role is changed the fc class
will queue a scan and then call scsi_target_unblock. The problem
with this is if the devices are in the SDEV_OFFLINE state and
the scan is run before the scsi_target_unblock, then the scan
will see LUN0 as offline and the scan will fail. This patch moves
the unblock call to before the scan, so we know the device state
will be set correctly when the scan is run.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>