mmc: sdhci-sprd: use sdhci_sprd_writew

The sdhci_sprd_writew() was defined by never used in sdhci_ops:

    drivers/mmc/host/sdhci-sprd.c:134:20: warning: unused function 'sdhci_sprd_writew'

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210601095403.236007-2-krzysztof.kozlowski@canonical.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>