x86/hpet: Pass proper pointer to irq_alloc_info

Fix the following oops:
 hpet_msi_get_hwirq+0x1f/0x27
 msi_domain_alloc+0x35/0xfe
 ? trace_hardirqs_on_caller+0x16c/0x188
 irq_domain_alloc_irqs_recursive+0x51/0x95
 __irq_domain_alloc_irqs+0x151/0x223
 hpet_assign_irq+0x5d/0x68
 hpet_msi_capability_lookup+0x121/0x1cb
 ? hpet_enable+0x2b4/0x2b4
 hpet_late_init+0x5f/0xf2
 ? hpet_enable+0x2b4/0x2b4
 do_one_initcall+0x184/0x199
 kernel_init_freeable+0x1af/0x237
 ? rest_init+0x13a/0x13a
 kernel_init+0xe/0xd4
 ret_from_fork+0x3f/0x70
 ? rest_init+0x13a/0x13a

Since 3cb96f0c ('x86/hpet: Enhance HPET IRQ to support
hierarchical irqdomains') hpet_msi_capability_lookup() uses
hpet_assign_irq(). The latter initializes irq_alloc_info on stack, but
passes a NULL pointer to irq_domain_alloc_irqs(), which causes a NULL
pointer dereference later in hpet_msi_get_hwirq().

Pass the pointer to the irq_alloc_info irq_domain_alloc_irqs().

Fixes: 3cb96f0c

 'x86/hpet: Enhance HPET IRQ to support hierarchical irqdomains'
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Link: http://lkml.kernel.org/r/20150512041444.GA1094@swordfish
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>