mmc: core: Don't export the to_sdio_driver macro

The macro is only used by the mmc core, so let's move it in there.

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

drivers/mmc/core/sdio_bus.c

@@ -26,6 +26,8 @@
 #include "sdio_cis.h"
 #include "sdio_bus.h"
 
+#define to_sdio_driver(d)	container_of(d, struct sdio_driver, drv)
+
 /* show configuration fields */
 #define sdio_config_attr(field, format_string)				\
 static ssize_t								\