[ARM] oprofile: avoid lockdep warnings on mpcore oprofile init

Fix lockdep warnings, caused by 'set_affinity' being called without
the correct locks taken and local interrupts disabled:

=================================
[ INFO: inconsistent lock state ]
2.6.22-rc2 #1
---------------------------------
inconsistent {in-hardirq-W} -> {hardirq-on-W} usage.
swapper/1 [HC0[0]:SC0[0]:HE1:SE1] takes:
(irq_controller_lock){++..}, at: [<c002be50>] gic_set_cpu+0x60/0xa0
{in-hardirq-W} state was registered at:
 [<c005d9a8>] lock_acquire+0x58/0x6c
 [<c0233068>] _spin_lock+0x40/0x50
 [<c002c020>] gic_mask_irq+0x2c/0x6c
 [<c0069c64>] handle_level_irq+0x11c/0x14c
 [<c0020060>] asm_do_IRQ+0x60/0x84
 [<c0020d2c>] __irq_svc+0x4c/0xc0
 [<c000ed84>] __alloc_bootmem_nopanic+0x74/0x88
 [<c000edb0>] __alloc_bootmem+0x18/0x3c
 [<c000fa00>] alloc_large_system_hash+0x16c/0x200
 [<c00108dc>] inode_init_early+0x5c/0xa4
 [<c00106dc>] vfs_caches_init_early+0x24/0xa0
 [<c0008e54>] start_kernel+0x220/0x2fc
 [<00008078>] 0x8078
irq event stamp: 88438
hardirqs last  enabled at (88438): [<c0020dc0>] preempt_return+0x20/0x2c
hardirqs last disabled at (88436): [<c00417bc>] __do_softirq+0xb0/0x138
softirqs last  enabled at (88437): [<c0041810>] __do_softirq+0x104/0x138
softirqs last disabled at (88428): [<c0041d9c>] irq_exit+0x68/0x7c

other info that might help us debug this:
no locks held by swapper/1.

stack backtrace:
[<c0025ecc>] (dump_stack+0x0/0x14) from [<c005b1e4>] (print_usage_bug+0x138/0x168)
[<c005b0ac>] (print_usage_bug+0x0/0x168) from [<c005be80>] (mark_lock+0x484/0x6a0)
[<c005b9fc>] (mark_lock+0x0/0x6a0) from [<c005cc48>] (__lock_acquire+0x3c0/0x10c8)
[<c005c888>] (__lock_acquire+0x0/0x10c8) from [<c005d9a8>] (lock_acquire+0x58/0x6c)
[<c005d950>] (lock_acquire+0x0/0x6c) from [<c0233068>] (_spin_lock+0x40/0x50)
[<c0233028>] (_spin_lock+0x0/0x50) from [<c002be50>] (gic_set_cpu+0x60/0xa0)
[<c002bdf0>] (gic_set_cpu+0x0/0xa0) from [<c01b04cc>] (em_route_irq+0x38/0x40)
[<c01b0494>] (em_route_irq+0x0/0x40) from [<c01b04ec>] (em_setup+0x18/0xa4)
[<c01b04d4>] (em_setup+0x0/0xa4) from [<c001570c>] (oprofile_arch_init+0x24/0xe8)
[<c00156e8>] (oprofile_arch_init+0x0/0xe8) from [<c0015640>] (oprofile_init+0x1c/0x64)
[<c0015624>] (oprofile_init+0x0/0x64) from [<c0008a20>] (kernel_init+0x154/0x368)
[<c00088cc>] (kernel_init+0x0/0x368) from [<c003ef34>] (do_exit+0x0/0x904)
oprofile: using arm/mpcore
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/oprofile/op_model_mpcore.c

@@ -257,8 +257,13 @@ static void em_stop(void)
  */
 static void em_route_irq(int irq, unsigned int cpu)
 {
-	irq_desc[irq].affinity = cpumask_of_cpu(cpu);
-	irq_desc[irq].chip->set_affinity(irq, cpumask_of_cpu(cpu));
+	struct irq_desc *desc = irq_desc + irq;
+	cpumask_t mask = cpumask_of_cpu(cpu);
+
+	spin_lock_irq(&desc->lock);
+	desc->affinity = mask;
+	desc->chip->set_affinity(irq, mask);
+	spin_unlock_irq(&desc->lock);
 }
 
 static int em_setup(void)