tests/ioctl_mtd.c: fix build with musl

* tests/ioctl_mtd.c: Include <linux/ioctl.h>.
diff --git a/tests/ioctl_mtd.c b/tests/ioctl_mtd.c
index d7f7622..b761da8 100644
--- a/tests/ioctl_mtd.c
+++ b/tests/ioctl_mtd.c
@@ -34,6 +34,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <linux/ioctl.h>
 #include <linux/version.h>
 #if LINUX_VERSION_CODE < KERNEL_VERSION(3, 3, 0)
 # include "mtd-abi.h"