btrfs: cleanup device states define BTRFS_DEV_STATE_MISSING

Currently device state is being managed by each individual int
variable such as struct btrfs_device::missing. Instead of that
declare btrfs_device::dev_state BTRFS_DEV_STATE_MISSING and use
the bit operations.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by : Nikolay Borisov <nborisov@suse.com>
[ whitespace adjustments ]
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index d290641..68affb0 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -49,6 +49,7 @@ struct btrfs_pending_bios {
 
 #define BTRFS_DEV_STATE_WRITEABLE	(0)
 #define BTRFS_DEV_STATE_IN_FS_METADATA	(1)
+#define BTRFS_DEV_STATE_MISSING		(2)
 
 struct btrfs_device {
 	struct list_head dev_list;
@@ -73,7 +74,6 @@ struct btrfs_device {
 	fmode_t mode;
 
 	unsigned long dev_state;
-	int missing;
 	int is_tgtdev_for_dev_replace;
 	blk_status_t last_flush_error;
 	int flush_bio_sent;