LU-7581 ldiskfs: wrong EA inode backpointer check

LU-7581 ldiskfs: wrong EA inode backpointer check

EA inode is linked back to the parent inode using
i_mtime.tv_sec filed. An inode number bigger 2G gets
mangled due to sign bit extension over the high bits
of tv_sec. It causes parent backpointer checks to fail.
Add an explicit integer type conversion to ignore high
bits of i_mtime.tv_sec.

Change-Id: I4e086ca5bf13ec77ef0af73fa1f88846e278de23
Seagate-bug-id: MRP-3215
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@seagate.com>
Reviewed-on: http://review.whamcloud.com/17675
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>