mmc: sdhci-pci: Make function amd_sdhci_reset static

Fix sparse warnings:

drivers/mmc/host/sdhci-pci-core.c:1599:6: warning: symbol 'amd_sdhci_reset' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>