cpumask: remove cpumask allocation from idle_balance, fix

Impact: fix boot crash

Fix typo in the size calculation.
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <alpine.DEB.2.00.0903181729360.31583@gandalf.stny.rr.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -8297,7 +8297,7 @@ void __init sched_init(void)
 	alloc_size *= 2;
 #endif
 #ifdef CONFIG_CPUMASK_OFFSTACK
-	alloc_size *= num_possible_cpus() * cpumask_size();
+	alloc_size += num_possible_cpus() * cpumask_size();
 #endif
 	/*
 	 * As sched_init() is called before page_alloc is setup,