[MIPS] No need to write c0_compare in plat_timer_setup

If R4k counter was used for hpt_timer and interrupt source,
c0_hpt_timer_init() initializes the c0_compare register.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>