scsi: target: core: Use RCU helpers for INQUIRY t10_alua_tg_pt_gp

Fix the sparse warnings about t10_alua_tg_pt_gp accesses in
target_core_spc.c caused by commit 7324f47 ("scsi: target: Replace
lun_tg_pt_gp_lock with rcu in I/O path")

That commit replaced the lun_tg_pt_gp_lock use in the I/O path, but it
didn't update the INQUIRY code.

Link: https://lore.kernel.org/r/20211117213928.8634-1-michael.christie@oracle.com
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: mikechristie

drivers/target/target_core_spc.c

@@ -40,11 +40,11 @@ static void spc_fill_alua_data(struct se_lun *lun, unsigned char *buf)
 	 *
 	 * See spc4r17 section 6.4.2 Table 135
 	 */
-	spin_lock(&lun->lun_tg_pt_gp_lock);
-	tg_pt_gp = lun->lun_tg_pt_gp;
+	rcu_read_lock();
+	tg_pt_gp = rcu_dereference(lun->lun_tg_pt_gp);
 	if (tg_pt_gp)
 		buf[5] |= tg_pt_gp->tg_pt_gp_alua_access_type;
-	spin_unlock(&lun->lun_tg_pt_gp_lock);
+	rcu_read_unlock();
 }
 
 static u16
@@ -325,14 +325,14 @@ spc_emulate_evpd_83(struct se_cmd *cmd, unsigned char *buf)
 		 * Get the PROTOCOL IDENTIFIER as defined by spc4r17
 		 * section 7.5.1 Table 362
 		 */
-		spin_lock(&lun->lun_tg_pt_gp_lock);
-		tg_pt_gp = lun->lun_tg_pt_gp;
+		rcu_read_lock();
+		tg_pt_gp = rcu_dereference(lun->lun_tg_pt_gp);
 		if (!tg_pt_gp) {
-			spin_unlock(&lun->lun_tg_pt_gp_lock);
+			rcu_read_unlock();
 			goto check_lu_gp;
 		}
 		tg_pt_gp_id = tg_pt_gp->tg_pt_gp_id;
-		spin_unlock(&lun->lun_tg_pt_gp_lock);
+		rcu_read_unlock();
 
 		buf[off] = tpg->proto_id << 4;
 		buf[off++] |= 0x1; /* CODE SET == Binary */