usb: gadget: gadgetfs: Free memory allocated by memdup_user()

commit b44be246 upstream.

Commit 3b74c73f switched over to memdup_user()
in ep_write() function and removed kfree (kbuf).
memdup_user() function allocates memory which is never freed.

Fixes: 3b74c73f (usb: gadget: inode: switch over to memdup_user())
Signed-off-by: Mario Schuknecht <mario.schuknecht@dresearch-fe.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
[ luis: backported to 3.16:
  - file rename: drivers/usb/gadget/legacy/inode.c ->
    drivers/usb/gadget/inode.c ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/usb/gadget/inode.c

@@ -450,6 +450,7 @@ ep_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 		data->name, len, (int) value);
 free1:
 	mutex_unlock(&data->lock);
+	kfree (kbuf);
 	return value;
 }