clocksource: kona: fix __iomem annotation

It makes no sense to hide the __iomem annotation from the function
that uses it, especially since it causes a sparse warning:

drivers/clocksource/bcm_kona_timer.c:118:38: warning: incorrect type in argument 1 (different address spaces)
drivers/clocksource/bcm_kona_timer.c:118:38:    expected void *timer_base
drivers/clocksource/bcm_kona_timer.c:118:38:    got void [noderef] <asn:2>*static [toplevel] tmr_regs

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>