dm cache metadata: Fix loading discard bitset

Add missing dm_bitset_cursor_next() to properly advance the bitset
cursor.

Otherwise, the discarded state of all blocks is set according to the
discarded state of the first block.

Fixes: ae4a46a1 ("dm cache metadata: use bitset cursor api to load discard bitset")
Cc: stable@vger.kernel.org
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-cache-metadata.c

@@ -1167,11 +1167,18 @@ static int __load_discards(struct dm_cache_metadata *cmd,
 		if (r)
 			return r;
 
-		for (b = 0; b < from_dblock(cmd->discard_nr_blocks); b++) {
+		for (b = 0; ; b++) {
 			r = fn(context, cmd->discard_block_size, to_dblock(b),
 			       dm_bitset_cursor_get_value(&c));
 			if (r)
 				break;
+
+			if (b >= (from_dblock(cmd->discard_nr_blocks) - 1))
+				break;
+
+			r = dm_bitset_cursor_next(&c);
+			if (r)
+				break;
 		}
 
 		dm_bitset_cursor_end(&c);