LU-9735 compat: heed the fs_struct::seq

LU-9735 compat: heed the fs_struct::seq

2.6.37 kernel uses a seqlock in the fs_struct to enable us to take
an atomic copy of the complete cwd and root paths.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I35384b8f5c468a8c142a59032f3148b698a0c79e
Reviewed-on: https://review.whamcloud.com/28907
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>