ARM: OMAP2+: Fix build warning when mmc_omap is not built

GCC reports the following warning with W=1:

arch/arm/mach-omap2/board-n8x0.c:325:19: warning:
variable 'index' set but not used [-Wunused-but-set-variable]
325 |  int bit, *openp, index;
    |                   ^~~~~

Fix this by moving CONFIG_MMC_OMAP to cover the rest codes
in the n8x0_mmc_callback().
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/board-n8x0.c

@@ -322,6 +322,7 @@ static int n8x0_mmc_get_cover_state(struct device *dev, int slot)
 
 static void n8x0_mmc_callback(void *data, u8 card_mask)
 {
+#ifdef CONFIG_MMC_OMAP
 	int bit, *openp, index;
 
 	if (board_is_n800()) {
@@ -339,7 +340,6 @@ static void n8x0_mmc_callback(void *data, u8 card_mask)
 	else
 		*openp = 0;
 
-#ifdef CONFIG_MMC_OMAP
 	omap_mmc_notify_cover_event(mmc_device, index, *openp);
 #else
 	pr_warn("MMC: notify cover event not available\n");