[SCSI] fix regression that accidentally disabled block-based tcq

The scsi blk-mq support accidentally flipped a conditional, which lead to
never enabling block based tcq when using the legacy request path.

Fixes: d285203c scsi: add support for a blk-mq based I/O path.
Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>