mmc: remove unncessary mmc_gpio_free_cd() call from slot-gpio users

Since slot-gpio uses devm_* managed functions in mmc_gpio_request_cd()
now, we can remove those mmc_gpio_free_cd() call from host drivers'
.probe() error path and .remove().

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>