ata: mark expected switch fall-throughs

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

In cases where a "drop through" comment was already in place, I replaced
it  with a proper "fall through" comment, which is what GCC is expecting
to find.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 49b3745..e070fe8 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -3711,9 +3711,11 @@ static int ata_eh_handle_dev_fail(struct ata_device *dev, int err)
 	case -ENODEV:
 		/* device missing or wrong IDENTIFY data, schedule probing */
 		ehc->i.probe_mask |= (1 << dev->devno);
+		/* fall through */
 	case -EINVAL:
 		/* give it just one more chance */
 		ehc->tries[dev->devno] = min(ehc->tries[dev->devno], 1);
+		/* fall through */
 	case -EIO:
 		if (ehc->tries[dev->devno] == 1) {
 			/* This is the last chance, better to slow