VIM3: mmc_get_env_dev correct non emmc boot sources

need return -1 if boot source is not EMMC or SD ( for example it will be
useful if we have multy env sources configuration and device was booted
from SPI flash and env need read from SPI not from mmc )
Signed-off-by: NArtem Lapkin <art@khadas.com>
Reviewed-by: NJaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>

board/amlogic/vim3/vim3.c

@@ -19,9 +19,15 @@
 
 int mmc_get_env_dev(void)
 {
-	if (meson_get_boot_device() == BOOT_DEVICE_EMMC)
+	switch (meson_get_boot_device()) {
+	case BOOT_DEVICE_EMMC:
 		return 2;
-	return 1;
+	case BOOT_DEVICE_SD:
+		return 1;
+	default:
+		/* boot device is not EMMC|SD */
+		return -1;
+	}
 }
 
 /*