afs: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple fallthrough pseudo-keywords in
places where the code is intended to fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: David Howells <[e-mail]>
Reviewed-by: Jeffrey Altman <[e-mail]>
cc: [e-mail]
cc: [e-mail]
Link: https://lore.kernel.org/r/51[e-mail]/ # v1
Link: https://lore.kernel.org/r/20210420211615.GA51432@embeddedor/ # v2
Signed-off-by: Linus Torvalds <[e-mail]>

fs/afs/cmservice.c

···
 			return ret;
 
 		call->unmarshall++;
+		fallthrough;
+
 	case 5:
 		break;
 	}
···
 			r->node[loop] = ntohl(b[loop + 5]);
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 2:
 		break;
···
 			r->node[loop] = ntohl(b[loop + 5]);
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 2:
 		break;
···
 
 		afs_extract_to_tmp(call);
 		call->unmarshall++;
+		fallthrough;
 
 	case 3:
 		break;

fs/afs/fsclient.c

···
 		req->file_size = vp->scb.status.size;
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 5:
 		break;
···
 		_debug("motd '%s'", p);
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 8:
 		break;
···
 		xdr_decode_AFSVolSync(&bp, &op->volsync);
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 6:
 		break;
···
 		xdr_decode_AFSVolSync(&bp, &op->volsync);
 
 		call->unmarshall++;
+		fallthrough;
 
 	case 4:
 		break;

fs/afs/vlclient.c

···
 		if (ret < 0)
 			return ret;
 		call->unmarshall = 6;
+		fallthrough;
 
 	case 6:
 		break;