pnfs/blocklayout: put deviceid node after releasing bl_ext_lock

The last put of deviceid nodes for SCSI layouts may sleep, so we shouldn't
hold any spinlocks.  Make sure we put them outside the bl_ext_lock.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>