LU-2743 llite: Fix a negative hpk_errval assignment

LU-2743 llite: Fix a negative hpk_errval assignment

The hpk_errval field should store positve errnos.  This patch fixes a
place where errnos are assigned to hpk_errval as negative numbers.

Change-Id: I77b1f9e6a19a64aedcdcc5fe38b08babb810a472
Signed-off-by: Li Wei <wei.g.li@intel.com>
Reviewed-on: http://review.whamcloud.com/5729
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>