[PARISC] Prevent processor_probe() from clobbering cpu_data[0]

processor_probe() shouldn't clobber cpu_data[0]
cpu_data[0].it_value (used by timer_interrupt()) is already set.

Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>