MMC: OMAP: Check the get_cover_state function pointer if not set

If the get_cover_state is not set, it occurs the oops.
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/host/omap.c

@@ -236,7 +236,10 @@ static void mmc_omap_release_slot(struct mmc_omap_slot *slot)
 static inline
 int mmc_omap_cover_is_open(struct mmc_omap_slot *slot)
 {
-	return slot->pdata->get_cover_state(mmc_dev(slot->mmc), slot->id);
+	if (slot->pdata->get_cover_state)
+		return slot->pdata->get_cover_state(mmc_dev(slot->mmc),
+						    slot->id);
+	return 0;
 }
 
 static ssize_t