USB: gadgetfs: Fix a potential memory leak in 'dev_config()'

'kbuf' is allocated just a few lines above using 'memdup_user()'.
If the 'if (dev->buf)' test fails, this memory is never released.
Signed-off-by: NChristophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/legacy/inode.c

@@ -1782,8 +1782,10 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 
 	spin_lock_irq (&dev->lock);
 	value = -EINVAL;
-	if (dev->buf)
+	if (dev->buf) {
+		kfree(kbuf);
 		goto fail;
+	}
 	dev->buf = kbuf;
 
 	/* full or low speed config */