scsi: ufs: core: Fix single doorbell mode support

Commit 22089c218037 ("scsi: ufs: core: Optimize the hot path")
accidentally broke support for the legacy single doorbell mode. The
tag_set.shared_tags pointer is only != NULL if shared tag support is
enabled. The UFS driver only enables shared tag support in MCQ mode.

Fix this by handling legacy and MCQ modes differently in
ufshcd_tag_to_cmd().

Reported-by: Marek Szyprowski <[e-mail]>
Closes: https://lore.kernel.org/linux-scsi/[e-mail]/
Reported-by: André Draszik <[e-mail]>
Closes: https://lore.kernel.org/linux-scsi/[e-mail]/
Tested-by: Marek Szyprowski <[e-mail]>
Fixes: 22089c218037 ("scsi: ufs: core: Optimize the hot path")
Signed-off-by: Bart Van Assche <[e-mail]>
Tested-by: André Draszik <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/ufs/core/ufshcd-priv.h

···
  */
 static inline struct scsi_cmnd *ufshcd_tag_to_cmd(struct ufs_hba *hba, u32 tag)
 {
-	struct blk_mq_tags *tags = hba->host->tag_set.shared_tags;
+	/*
+	 * Host-wide tags are enabled in MCQ mode only. See also the
+	 * host->host_tagset assignment in ufs-mcq.c.
+	 */
+	struct blk_mq_tags *tags = hba->host->tag_set.shared_tags ?:
+					   hba->host->tag_set.tags[0];
 	struct request *rq = blk_mq_tag_to_rq(tags, tag);
 
 	if (WARN_ON_ONCE(!rq))