staging/lustre/llite: clear inode timestamps after losing UPDATE lock

Otherwise, those leftovers would interfere with new timestamps
especially when the timestamps are set back in time on the other
clients.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-on: http://review.whamcloud.com/22623
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8446


Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>