mmc: sdhci-pci: use generic sdhci_set_bus_width()

Now that sdhci_set_bus_width() supports 8-bit bus widths based on the
MMC_CAP_8_BIT_DATA capability flag, replace the sdhci-pci version with
the generic sdhci version.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>