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/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index a651e82..e3726ac 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1138,7 +1138,8 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 			nilfs_sc_cstage_set(sci, NILFS_ST_DAT);
 			goto dat_stage;
 		}
-		nilfs_sc_cstage_inc(sci);  /* Fall through */
+		nilfs_sc_cstage_inc(sci);
+		fallthrough;
 	case NILFS_ST_GC:
 		if (nilfs_doing_gc()) {
 			head = &sci->sc_gc_inodes;
@@ -1159,7 +1160,8 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 			}
 			sci->sc_stage.gc_inode_ptr = NULL;
 		}
-		nilfs_sc_cstage_inc(sci);  /* Fall through */
+		nilfs_sc_cstage_inc(sci);
+		fallthrough;
 	case NILFS_ST_FILE:
 		head = &sci->sc_dirty_files;
 		ii = list_prepare_entry(sci->sc_stage.dirty_file_ptr, head,
@@ -1186,7 +1188,7 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 		}
 		nilfs_sc_cstage_inc(sci);
 		sci->sc_stage.flags |= NILFS_CF_IFILE_STARTED;
-		/* Fall through */
+		fallthrough;
 	case NILFS_ST_IFILE:
 		err = nilfs_segctor_scan_file(sci, sci->sc_root->ifile,
 					      &nilfs_sc_file_ops);
@@ -1197,13 +1199,14 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 		err = nilfs_segctor_create_checkpoint(sci);
 		if (unlikely(err))
 			break;
-		/* Fall through */
+		fallthrough;
 	case NILFS_ST_CPFILE:
 		err = nilfs_segctor_scan_file(sci, nilfs->ns_cpfile,
 					      &nilfs_sc_file_ops);
 		if (unlikely(err))
 			break;
-		nilfs_sc_cstage_inc(sci);  /* Fall through */
+		nilfs_sc_cstage_inc(sci);
+		fallthrough;
 	case NILFS_ST_SUFILE:
 		err = nilfs_sufile_freev(nilfs->ns_sufile, sci->sc_freesegs,
 					 sci->sc_nfreesegs, &ndone);
@@ -1219,7 +1222,8 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 					      &nilfs_sc_file_ops);
 		if (unlikely(err))
 			break;
-		nilfs_sc_cstage_inc(sci);  /* Fall through */
+		nilfs_sc_cstage_inc(sci);
+		fallthrough;
 	case NILFS_ST_DAT:
  dat_stage:
 		err = nilfs_segctor_scan_file(sci, nilfs->ns_dat,
@@ -1230,7 +1234,8 @@ static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
 			nilfs_sc_cstage_set(sci, NILFS_ST_DONE);
 			return 0;
 		}
-		nilfs_sc_cstage_inc(sci);  /* Fall through */
+		nilfs_sc_cstage_inc(sci);
+		fallthrough;
 	case NILFS_ST_SR:
 		if (mode == SC_LSEG_SR) {
 			/* Appending a super root */