scsi: t10-pi: Return correct ref tag when queue has no integrity profile

Commit ddd0bc75 ("block: move ref_tag calculation func to the block
layer") moved ref tag calculation from SCSI to a library function. However,
this change broke returning the correct ref tag for devices operating in
DIF mode since these do not have an associated block integrity profile.
This in turn caused read/write failures on PI-formatted disks attached to
an mpt3sas controller.

Fixes: ddd0bc75

 ("block: move ref_tag calculation func to the block layer")
Cc: stable@vger.kernel.org # 4.19+
Reported-by: John Garry <john.garry@huawei.com>
Tested-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>