[SPARC64]: Fix booting on non-zero cpu.

The early per-cpu handling needs a slight tweak to work when booting
on a non-zero cpu.

We got away with this for a long time, but can't any longer as now
even printk() calls functions (cpu_clock() for example) that thus make
early references to per-cpu variables.

Signed-off-by: David S. Miller <davem@davemloft.net>