ARM: mach-shmobile: sh73a0 twd_base fix

Fix the case of too late twd_base initialization for SMP
on sh73a0 which bas been broken because sh73a0 specific
smp_prepare_cpu() and percpu_timer_setup() changed order
in the commits:

05c74a6c
c413521e

Without this fix the sh73a0 SMP kernel panics on boot.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>