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/disk-io.c b/fs/btrfs/disk-io.c
index 44573cd..4f7d2a3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3389,7 +3389,7 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
 	/* send down all the barriers */
 	head = &info->fs_devices->devices;
 	list_for_each_entry(dev, head, dev_list) {
-		if (dev->missing)
+		if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state))
 			continue;
 		if (!dev->bdev)
 			continue;
@@ -3403,7 +3403,7 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
 
 	/* wait for all the barriers */
 	list_for_each_entry(dev, head, dev_list) {
-		if (dev->missing)
+		if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state))
 			continue;
 		if (!dev->bdev) {
 			errors_wait++;