mmc: mmci: rename sdio flag in vendor data to st_sdio

This patch renames sdio flag in vendor data to st_sdio, as this flag is
only used to enable ST specific sdio setup. This will also ensure that
the ST specfic setup is not done on other vendor like Qualcomm.

Originally the issue was detected while testing WLAN ath6kl on IFC6410
board with APQ8064 SOC.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>