[VOYAGER] clockevents: correct boot cpu is zero assumption

This isn't true for voyager, so alter setup_pit_timer() to initialise
the cpumask from the current processor id (which should be the boot
processor) rather than defaulting to zero.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>