LU-4310 kernel: missed unlock in quota patch

LU-4310 kernel: missed unlock in quota patch

The quota-replace-dqptr-sem.patch introduced a regression which
could miss unlock inode->i_lock in __dquot_alloc_space().

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: If0f240fe76d661909c13b11e3d384e77da1662b1
Reviewed-on: http://review.whamcloud.com/8400
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Jenkins
Reviewed-by: Andrew Perepechko <andrew_perepechko@xyratex.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>