mmc: sdhci-s3c: remove unused ext_cd_gpio field

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/3f12c2deaae9e77a5e7ab8415db7751a27bc3b98.1575916477.git.mirq-linux@rere.qmqm.pl


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