IB/hfi1: Using kfree_rcu() to simplify the code

The callback function of call_rcu() just calls a kfree(), so we
can use kfree_rcu() instead of call_rcu() + callback function.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Tested-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Tested-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>