hikey: increase delay after eMMC initialized

Some eMMC chips require a longer delay. After testing
different chips, 20ms appears to work reliably.
Signed-off-by: Ryan Grachek <ryan@edited.us>

plat/hisilicon/hikey/hikey_bl2_setup.c

@@ -336,7 +336,7 @@ void bl2_platform_setup(void)
 	params.flags = MMC_FLAG_CMD23;
 	info.mmc_dev_type = MMC_IS_EMMC;
 	dw_mmc_init(&params, &info);
-	mdelay(5);
+	mdelay(20);
 
 	hikey_io_setup();
 }