staging: wilc1000: remove varialbe sdio_set_default_speed

This patch removes sdio_set_default_speed of wilc_wlan_io_func_t which is
not used anymore and also remove struct sdio since it is empty.
Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/linux_wlan.c

@@ -894,7 +894,6 @@ void linux_to_wlan(wilc_wlan_inp_t *nwi, struct wilc *nic)
 	nwi->io_func.io_type = HIF_SDIO;
 	nwi->io_func.io_init = linux_sdio_init;
 	nwi->io_func.io_deinit = linux_sdio_deinit;
-	nwi->io_func.u.sdio.sdio_set_default_speed = linux_sdio_set_default_speed;
 #else
 	nwi->io_func.io_type = HIF_SPI;
 	nwi->io_func.io_init = linux_spi_init;

drivers/staging/wilc1000/wilc_wlan_if.h

@@ -77,9 +77,6 @@ typedef struct {
 	int (*io_init)(void *);
 	void (*io_deinit)(void *);
 	union {
-		struct {
-			int (*sdio_set_default_speed)(void);
-		} sdio;
 		struct {
 			int (*spi_max_speed)(void);
 			int (*spi_tx)(u8 *, u32);