[POWERPC] iSeries: Fix unregistering HV event handlers

Commit fbd568a3e61a7decb8a754ad952aaa5b5c82e9e5 ("Change
synchronize_kernel to _rcu and _sched") changed the deprecated
synchronize_kernel() in HvLpEvent_unregisterHandler() to
synchronize_rcu().  It turns out that it should have been
synchronize_sched().

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/iseries/lpevents.c

@@ -226,7 +226,7 @@ int HvLpEvent_unregisterHandler(HvLpEvent_Type eventType)
 			 * other CPUs, and that the deleted handler isn't
 			 * still running on another CPU when we return.
 			 */
-			synchronize_rcu();
+			synchronize_sched();
 			return 0;
 		}
 	}