[S390] Fix uninitialized spinlock use

Ever since commit 43ca5c3a ([S390] Convert
monitor calls to function calls.), the kernel refused to IPL with spinlock
debugging enabled.

BUG: spinlock bad magic on CPU#0, swapper/0
 lock: 00000000003a4668, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
CPU: 0 Not tainted 2.6.25 #1
Process swapper (pid: 0, task: 000000000034f958, ksp: 0000000000377d60)
0000000000377ab8 0000000000352628 0000000000377d60 0000000000377d60
       0000000000016af4 00000000fffff7b5 0000000000377d60 0000000000000000
       0000000000000000 0000000000377a18 0000000000000009 0000000000377a18
       0000000000377a78 000000000023c920 0000000000016af4 0000000000377a18
       0000000000000005 0000000000000000 0000000000377b58 0000000000377ab8
Call Trace:
([<0000000000016a60>] show_trace+0xdc/0x108)
 [<0000000000016b4e>] show_stack+0xc2/0xfc
 [<0000000000016c9a>] dump_stack+0xb2/0xc0
 [<0000000000172dd4>]
Signed-off-by: NJosef 'Jeff' Sipek <jeffpc@josefsipek.net>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/process.c

@@ -75,7 +75,9 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
 	return sf->gprs[8];
 }
 
-DEFINE_PER_CPU(struct s390_idle_data, s390_idle);
+DEFINE_PER_CPU(struct s390_idle_data, s390_idle) = {
+	.lock = __SPIN_LOCK_UNLOCKED(s390_idle.lock)
+};
 
 static int s390_idle_enter(void)
 {