mmc: sdhci-pci-gli: Fix can not access GL9750 after reboot from Windows 10

Need to clear some bits in a vendor-defined register after reboot from
Windows 10.

Fixes: e51df6ce

 ("mmc: host: sdhci-pci: Add Genesys Logic GL975x support")
Reported-by: Grzegorz Kowal <custos.mentis@gmail.com>
Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Grzegorz Kowal <custos.mentis@gmail.com>
Link: https://lore.kernel.org/r/20200504063957.6638-1-benchuanggli@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>