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/locks.c b/fs/locks.c
index 8fc0542f..1f84a03 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1499,7 +1499,7 @@ static void lease_clear_pending(struct file_lock *fl, int arg)
 	switch (arg) {
 	case F_UNLCK:
 		fl->fl_flags &= ~FL_UNLOCK_PENDING;
-		/* fall through */
+		fallthrough;
 	case F_RDLCK:
 		fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
 	}
@@ -2525,7 +2525,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
 		cmd = F_SETLKW;
 		file_lock->fl_flags |= FL_OFDLCK;
 		file_lock->fl_owner = filp;
-		/* Fallthrough */
+		fallthrough;
 	case F_SETLKW:
 		file_lock->fl_flags |= FL_SLEEP;
 	}
@@ -2656,7 +2656,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
 		cmd = F_SETLKW64;
 		file_lock->fl_flags |= FL_OFDLCK;
 		file_lock->fl_owner = filp;
-		/* Fallthrough */
+		fallthrough;
 	case F_SETLKW64:
 		file_lock->fl_flags |= FL_SLEEP;
 	}