scsi: ppa: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 114988
Addresses-Coverity-ID: 114989
Addresses-Coverity-ID: 114990
Addresses-Coverity-ID: 114991
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/ppa.c

···
 			return 0;
 		}
 		cmd->SCp.phase++;
+		/* fall through */
 
 	case 3:		/* Phase 3 - Ready to accept a command */
 		w_ctr(ppb, 0x0c);
···
 		if (!ppa_send_command(cmd))
 			return 0;
 		cmd->SCp.phase++;
+		/* fall through */
 
 	case 4:		/* Phase 4 - Setup scatter/gather buffers */
 		if (scsi_bufflen(cmd)) {
···
 		}
 		cmd->SCp.buffers_residual = scsi_sg_count(cmd) - 1;
 		cmd->SCp.phase++;
+		/* fall through */
 
 	case 5:		/* Phase 5 - Data transfer stage */
 		w_ctr(ppb, 0x0c);
···
 		if (retv == 0)
 			return 1;
 		cmd->SCp.phase++;
+		/* fall through */
 
 	case 6:		/* Phase 6 - Read status/message */
 		cmd->result = DID_OK << 16;