btrfs: remove unnecessary variable shadowing in btrfs_invalidatepage()

In btrfs_invalidatepage() we re-declare @tree variable as
btrfs_ordered_inode_tree.

Since it's only used to do the spinlock, we can grab it from inode
directly, and remove the unnecessary declaration completely.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -8413,15 +8413,11 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
 		 * for the finish_ordered_io
 		 */
 		if (TestClearPagePrivate2(page)) {
-			struct btrfs_ordered_inode_tree *tree;
-
-			tree = &inode->ordered_tree;
-
-			spin_lock_irq(&tree->lock);
+			spin_lock_irq(&inode->ordered_tree.lock);
 			set_bit(BTRFS_ORDERED_TRUNCATED, &ordered->flags);
 			ordered->truncated_len = min(ordered->truncated_len,
 						     start - ordered->file_offset);
-			spin_unlock_irq(&tree->lock);
+			spin_unlock_irq(&inode->ordered_tree.lock);
 
 			if (btrfs_dec_test_ordered_pending(inode, &ordered,
 							   start,