reiserfs: fix race in readdir

jdm-20004 reiserfs_delete_xattrs: Couldn't delete all xattrs (-2)

The -ENOENT is due to readdir calling dir_emit on the same entry twice.

If the dir_emit callback sleeps and the tree is changed underneath us,
we won't be able to trust deh_offset(deh) anymore. We need to save
next_pos before we might sleep so we can find the next entry.

Change-Id: Id97ee4a32c57f313dab4b928d728a1cf2ede7602
CC: stable@vger.kernel.org
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>