mmc: sdhci: key 8BITBUS bit off MMC_CAP_8_BIT_DATA

Hosts supporting 8-bit bus are marked accordingly. If MMC_CAP_8_BIT_DATA
is not among host capabilities, 8BITBUS bit will never be set and it
is not cleared in case some non-SDHCI3 host uses it for something else.

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