dm: mmc: Set up the device pointer when using the MMC uclass

Update the existing drivers to set up this new pointer. This will be required
by the MMC uclass.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/mmc.h b/include/mmc.h
index f01674d..6d1f05c 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -381,6 +381,9 @@
 	char init_in_progress;	/* 1 if we have done mmc_start_init() */
 	char preinit;		/* start init as early as possible */
 	int ddr_mode;
+#ifdef CONFIG_DM_MMC
+	struct udevice *dev;	/* Device for this MMC controller */
+#endif
 };
 
 struct mmc_hwpart_conf {