clocksource/drivers/h8300_timer8: Fix wrong return value in h8300_8timer_init()

In the init function, if the call to of_iomap() fails, the return
value is ENXIO instead of -ENXIO.

Change to the right negative errno.

Fixes: 691f8f87 ("clocksource/drivers/h8300_timer8: Convert init function to return error")
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200802111541.5429-1-tianjia.zhang@linux.alibaba.com