btrfs: cleanup device states define BTRFS_DEV_STATE_REPLACE_TGT

Currently device state is being managed by each individual int
variable such as struct btrfs_device::is_tgtdev_for_dev_replace.
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>
[ whitespace adjustments ]
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index ba53245..84707e7 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1974,7 +1974,8 @@
 	list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
 		if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
 						&device->dev_state) ||
-		    !device->bdev || device->is_tgtdev_for_dev_replace)
+		    !device->bdev ||
+		    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
 			continue;
 
 		if (i >= nr_devices)