rockchip: configs: correct mmc env dev for rk3288 based boards

we are using mmc alias , so mmc index have been changed.
now mmc dev 0 is emmc and mmc dev 1 is sdmmc.

Signed-off-by: Jacob Chen <jacob2.chen@rock-chips.com>
diff --git a/include/configs/popmetal_rk3288.h b/include/configs/popmetal_rk3288.h
index 6a068bb..bbd54a1 100644
--- a/include/configs/popmetal_rk3288.h
+++ b/include/configs/popmetal_rk3288.h
@@ -11,7 +11,7 @@
 #include <configs/rk3288_common.h>
 
 #define CONFIG_ENV_IS_IN_MMC
-#define CONFIG_SYS_MMC_ENV_DEV 1
+#define CONFIG_SYS_MMC_ENV_DEV 0
 
 #define CONFIG_SYS_WHITE_ON_BLACK