Fix preemption warnings in speedstep-centrino.c

Fix preemption warnings in speedstep-centrino.c

BUG: using smp_processor_id() in preemptible [00000001] code:
kondemand/0/2473
caller is centrino_target+0xfb/0x600
[<401e3646>] debug_smp_processor_id+0x9e/0xb0
[<40112afb>] centrino_target+0xfb/0x600
[<40112a00>] centrino_target+0x0/0x600
[<40305bd9>] __cpufreq_driver_target+0x5c/0x6b
[<f897a537>] do_dbs_timer+0x1bc/0x208 [cpufreq_ondemand]
[<40134a46>] run_workqueue+0x85/0x125
[<40374f7f>] _spin_lock_irqsave+0x18/0x66
[<f897a37b>] do_dbs_timer+0x0/0x208 [cpufreq_ondemand]
[<401353fb>] worker_thread+0xf9/0x124
[<401213b9>] default_wake_function+0x0/0xc
[<40135302>] worker_thread+0x0/0x124
[<40137b37>] kthread+0xb0/0xd9
[<40137a87>] kthread+0x0/0xd9
[<40104b2f>] kernel_thread_helper+0x7/0x10

Signed-off-by: Dave Jones <davej@redhat.com>