LU-4336 quota: improper assert in osc_quota_chkdq()

In osc_quota_chkdq(), we should never try to access oqi found
from hash, since it could have been freed by osc_quota_setdq().

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: Ia73cf89cb5bbd730fa6f0a00e44771f733b2baa6