treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
diff --git a/drivers/scsi/53c700.c b/drivers/scsi/53c700.c
index 461b3ba..84b57a8 100644
--- a/drivers/scsi/53c700.c
+++ b/drivers/scsi/53c700.c
@@ -1832,7 +1832,7 @@ NCR_700_queuecommand_lck(struct scsi_cmnd *SCp, void (*done)(struct scsi_cmnd *)
 	case REQUEST_SENSE:
 		/* clear the internal sense magic */
 		SCp->cmnd[6] = 0;
-		/* fall through */
+		fallthrough;
 	default:
 		/* OK, get it from the command */
 		switch(SCp->sc_data_direction) {