Add missing includes.

Change-Id: I06ea08400efa511e627be37a4fd70fbdfadea2e6
diff --git a/minui/graphics_fbdev.c b/minui/graphics_fbdev.c
index c0c1bcb..a087899 100644
--- a/minui/graphics_fbdev.c
+++ b/minui/graphics_fbdev.c
@@ -16,6 +16,7 @@
 
 #include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
 #include <fcntl.h>