sandbox: enable CMD_WRITE

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
diff --git a/configs/sandbox64_defconfig b/configs/sandbox64_defconfig
index ccbc18a..b773781 100644
--- a/configs/sandbox64_defconfig
+++ b/configs/sandbox64_defconfig
@@ -58,6 +58,7 @@
 CONFIG_CMD_TEMPERATURE=y
 CONFIG_CMD_USB=y
 CONFIG_CMD_WDT=y
+CONFIG_CMD_WRITE=y
 CONFIG_CMD_CAT=y
 CONFIG_BOOTP_DNS2=y
 CONFIG_CMD_TFTPPUT=y