cmd_mmc: eliminate device num in the mmc command

mmc command applied device, like ide and usb...

Signed-off-by: Lei Wen <leiwen@marvell.com>
Acked-by: Andy Fleming <afleming@freescale.com>

drivers/mmc/mmc.c

@@ -1110,6 +1110,11 @@ void print_mmc_devices(char separator)
 	printf("\n");
 }
 
+int get_mmc_num(void)
+{
+	return cur_dev_num;
+}
+
 int mmc_initialize(bd_t *bis)
 {
 	INIT_LIST_HEAD (&mmc_devices);