ia64,rcu: Convert call_rcu(sn_irq_info_free) to kfree_rcu()

The rcu callback sn_irq_info_free() just calls a kfree(),
so we use kfree_rcu() instead of the call_rcu(sn_irq_info_free).

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>