Include stdlib in usb.c

As malloc is used

Signed-off-by: Henry-ZHR <henry-zhr@qq.com>

usb.c

@@ -2,6 +2,7 @@
 #include <fcntl.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <libusb.h>