scsi: use 'scsi_device_from_queue()' for scsi_dh

scsi: use 'scsi_device_from_queue()' for scsi_dh

BugLink: http://bugs.launchpad.net/bugs/1672544
commit 857de6e00778738dc3d61f75acbac35bdc48e533 upstream.

The device handler needs to check if a given queue belongs to a scsi
device; only then does it make sense to attach a device handler.

[mkp: dropped flags]

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>