mmc: sdhci-pci-o2micro: Make some symbols static

Fix the following sparse warning:

drivers/mmc/host/sdhci-pci-o2micro.c:497:6: warning: symbol
'sdhci_pci_o2_set_clock' was not declared. Should it be static?
drivers/mmc/host/sdhci-pci-o2micro.c:512:5: warning: symbol
'sdhci_pci_o2_probe_slot' was not declared. Should it be static?
drivers/mmc/host/sdhci-pci-o2micro.c:581:5: warning: symbol
'sdhci_pci_o2_probe' was not declared. Should it be static?
drivers/mmc/host/sdhci-pci-o2micro.c:786:5: warning: symbol
'sdhci_pci_o2_resume' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/1587624199-96926-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>