staging: mt7621-mmc: Fix null pointer deref if ext sdio irq enabled

The enable|disable_sdio_irq() fields of msdc_hw are never set, so when
they are called, they are null pointer. In case of the
MSDC_EXT_SDIO_IRQ flag set in msdc0_hw, this happens. But because
these fields are never set, they can simply be removed.
Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-mmc/board.h

@@ -68,10 +68,6 @@ struct msdc_hw {
 	/* external power control for card */
 	void (*ext_power_on)(void);
 	void (*ext_power_off)(void);
-
-	/* external sdio irq operations */
-	void (*enable_sdio_eirq)(void);
-	void (*disable_sdio_eirq)(void);
 };
 
 extern struct msdc_hw msdc0_hw;

drivers/staging/mt7621-mmc/sd.c

@@ -2261,10 +2261,6 @@ static void msdc_ops_enable_sdio_irq(struct mmc_host *mmc, int enable)
 	u32 tmp;
 
 	if (hw->flags & MSDC_EXT_SDIO_IRQ) { /* yes for sdio */
-		if (enable)
-			hw->enable_sdio_eirq();  /* combo_sdio_enable_eirq */
-		else
-			hw->disable_sdio_eirq(); /* combo_sdio_disable_eirq */
 	} else {
 		ERR_MSG("XXX ");  /* so never enter here */
 		tmp = sdr_read32(SDC_CFG);