btrfs: simplify btrfs_dev_replace_kthread

This function prints an informative message and then continues
dev-replace. The message contains a progress percentage which is read
from the status. The status is allocated dynamically, about 2600 bytes,
just to read the single value. That's an overkill. We'll use the new
helper and drop the allocation.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/dev-replace.c

@@ -809,25 +809,19 @@ static int btrfs_dev_replace_kthread(void *data)
 {
 	struct btrfs_fs_info *fs_info = data;
 	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
-	struct btrfs_ioctl_dev_replace_args *status_args;
 	u64 progress;
 
-	status_args = kzalloc(sizeof(*status_args), GFP_KERNEL);
-	if (status_args) {
-		btrfs_dev_replace_status(fs_info, status_args);
-		progress = status_args->status.progress_1000;
-		kfree(status_args);
+	progress = btrfs_dev_replace_progress(fs_info);
 	progress = div_u64(progress, 10);
 	btrfs_info_in_rcu(fs_info,
 		"continuing dev_replace from %s (devid %llu) to %s @%u%%",
-			dev_replace->srcdev->missing ? "<missing disk>" :
-			rcu_str_deref(dev_replace->srcdev->name),
+		dev_replace->srcdev->missing ? "<missing disk>"
+			: rcu_str_deref(dev_replace->srcdev->name),
 		dev_replace->srcdev->devid,
-			dev_replace->tgtdev ?
-			rcu_str_deref(dev_replace->tgtdev->name) :
-			"<missing target disk>",
+		dev_replace->tgtdev ? rcu_str_deref(dev_replace->tgtdev->name)
+			: "<missing target disk>",
 		(unsigned int)progress);
-	}
+
 	btrfs_dev_replace_continue_on_mount(fs_info);
 	clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);