bcachefs: Add missing bch2_trans_iter_exit() call

This fixes a bug where the filesystem goes read only when reading from
debugfs.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/debug.c

@@ -406,6 +406,8 @@ static ssize_t bch2_read_bfloat_failed(struct file *file, char __user *buf,
 		if (!i->size)
 			break;
 	}
+	bch2_trans_iter_exit(&trans, &iter);
+
 	bch2_trans_exit(&trans);
 
 	return err < 0 ? err : i->ret;