drbd: Mark expected switch fall-throughs

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

This patch fixes the following warnings:

In file included from drivers/block/drbd/drbd_actlog.c:30:
drivers/block/drbd/drbd_int.h: In function ‘__drbd_chk_io_error_’:
drivers/block/drbd/drbd_int.h:1774:6: warning: this statement may fall through [-Wimplicit-fallthrough=]

   if (df == DRBD_READ_ERROR || df == DRBD_WRITE_ERROR) {
      ^

drivers/block/drbd/drbd_int.h:1782:2: note: here
case EP_DETACH:
^~~~
drivers/block/drbd/drbd_req.c: In function ‘__req_mod’:
drivers/block/drbd/drbd_req.c:856:6: warning: this statement may fall through [-Wimplicit-fallthrough=]

   if (!(req->rq_state & RQ_NET_OK)) {
      ^

CC [M] fs/btrfs/inode-map.o
drivers/block/drbd/drbd_req.c:871:2: note: here
case BARRIER_ACKED:
^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

Notice that in some cases, the code comment is modified in accordance with what GCC is expecting to find.

This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough.

---
 drivers/block/drbd/drbd_int.h | 2 +-
 drivers/block/drbd/drbd_req.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

index 000a2f4c0e92..f070f7200fc0 100644
@@ -1778,7 +1778,7 @@ static inline void __drbd_chk_io_error_(struct drbd_device *device,
 				_drbd_set_state(_NS(device, disk, D_INCONSISTENT), CS_HARD, NULL);
 			break;
 		}
-		/* NOTE fall through for DRBD_META_IO_ERROR or DRBD_FORCE_DETACH */
+		/* fall through - for DRBD_META_IO_ERROR or DRBD_FORCE_DETACH */
 	case EP_DETACH:
 	case EP_CALL_HELPER:
 		/* Remember whether we saw a READ or WRITE error.

index 643a04af213b..3809c7e6be8c 100644
@@ -866,7 +866,7 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 			} /* else: FIXME can this happen? */
 			break;
 		}
-		/* else, fall through to BARRIER_ACKED */
+		/* else, fall through - to BARRIER_ACKED */
 
 	case BARRIER_ACKED:
 		/* barrier ack for READ requests does not make sense */

2.20.1