LU-7315 osd-ldiskfs: handle pdo lock properly

LU-7315 osd-ldiskfs: handle pdo lock properly

Inside the osd_dirent_check_repair(), if the logic comes to
"goto again", it only unlock the "hlock" but without seting
the variable @hlock as NULL. Althouth it will not cause any
logic failure, it may make the readers to be confused. This
patch will set "hlock = NULL;" explicitly to avoid trouble.

On the other hand, inside ldiskfs, the pdo lock users need
to check whether the lock handler is NULL or not properly.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I9db9dc758a2976849c299f76e06723e796da235d
Reviewed-on: http://review.whamcloud.com/16924
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Liang Zhen <liang.zhen@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>