usb: Minor - properly free memory on get_device_config() error path

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/src/hw/usb.c b/src/hw/usb.c
index 46e17df..1b4ea8b 100644
--- a/src/hw/usb.c
+++ b/src/hw/usb.c
@@ -253,8 +253,10 @@
         return NULL;
     req.wLength = cfg.wTotalLength;
     ret = usb_send_default_control(pipe, &req, config);
-    if (ret)
+    if (ret) {
+        free(config);
         return NULL;
+    }
     //hexdump(config, cfg.wTotalLength);
     return config;
 }