ocfs2: Reset status if we want to restart file extension.

In __ocfs2_extend_allocation, we will restart our file extension
if ((!status) && restart_func). But there is a bug that the
status is still left as -EGAIN. This is really an old bug,
but it is masked by the return value of ocfs2_journal_dirty.
So it show up when we make ocfs2_journal_dirty void.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>