platform/x86: ISST: Mark mmio_range_devid_0 and mmio_range_devid_1 with static keyword

platform/x86: ISST: Mark mmio_range_devid_0 and mmio_range_devid_1 with static keyword

Fix the following sparse warnings:

drivers/platform/x86/intel_speed_select_if/isst_if_mmio.c:23:24: warning: symbol 'mmio_range_devid_0' was not declared. Should it be static?
drivers/platform/x86/intel_speed_select_if/isst_if_mmio.c:28:24: warning: symbol 'mmio_range_devid_1' was not declared. Should it be static?

Signed-off-by: Zou Wei <zou_wei@huawei.com>
Link: https://lore.kernel.org/r/1607430489-116200-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>