Add missing headers for compilation on x86 targets

Change-Id: I5f4dc797b353a0f01fa00d38375ec303bf863254
diff --git a/toolbox/nandread.c b/toolbox/nandread.c
index 9644973..b124731 100644
--- a/toolbox/nandread.c
+++ b/toolbox/nandread.c
@@ -4,6 +4,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <unistd.h>
 
 #include <mtd/mtd-user.h>
 #include <sys/ioctl.h>
@@ -283,4 +284,3 @@
 
     return 0;
 }
-