target: Suppress gcc 7 fallthrough warnings

Avoid that gcc 7 reports the following warning when building with W=1:

warning: this statement may fall through [-Wimplicit-fallthrough=]
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Varun Prakash <varun@chelsio.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/cxgbit/cxgbit_main.c

@@ -446,6 +446,7 @@ cxgbit_uld_lro_rx_handler(void *hndl, const __be64 *rsp,
 	case CPL_RX_ISCSI_DDP:
 	case CPL_FW4_ACK:
 		lro_flush = false;
+		/* fall through */
 	case CPL_ABORT_RPL_RSS:
 	case CPL_PASS_ESTABLISH:
 	case CPL_PEER_CLOSE:

drivers/target/target_core_pr.c

@@ -353,6 +353,7 @@ static int core_scsi3_pr_seq_non_holder(struct se_cmd *cmd, u32 pr_reg_type,
 		break;
 	case PR_TYPE_WRITE_EXCLUSIVE_REGONLY:
 		we = 1;
+		/* fall through */
 	case PR_TYPE_EXCLUSIVE_ACCESS_REGONLY:
 		/*
 		 * Some commands are only allowed for registered I_T Nexuses.
@@ -361,6 +362,7 @@ static int core_scsi3_pr_seq_non_holder(struct se_cmd *cmd, u32 pr_reg_type,
 		break;
 	case PR_TYPE_WRITE_EXCLUSIVE_ALLREG:
 		we = 1;
+		/* fall through */
 	case PR_TYPE_EXCLUSIVE_ACCESS_ALLREG:
 		/*
 		 * Each registered I_T Nexus is a reservation holder.

drivers/target/target_core_transport.c

@@ -2092,7 +2092,7 @@ static void transport_complete_qf(struct se_cmd *cmd)
 			ret = cmd->se_tfo->queue_data_in(cmd);
 			break;
 		}
-		/* Fall through for DMA_TO_DEVICE */
+		/* fall through */
 	case DMA_NONE:
 queue_status:
 		trace_target_cmd_complete(cmd);
@@ -2270,7 +2270,7 @@ static void target_complete_ok_work(struct work_struct *work)
 				goto queue_full;
 			break;
 		}
-		/* Fall through for DMA_TO_DEVICE */
+		/* fall through */
 	case DMA_NONE:
 queue_status:
 		trace_target_cmd_complete(cmd);