[nrf fromtree] usb: device_next: msc: Do not leak SCSI buffer on dequeue

Multiple submitted requests are getting merged to single cancelled
net_buf on endpoint dequeue. While MSC class was correctly decrementing
the usage counters, it was not freeing SCSI buffer pointed to by frags.

Signed-off-by: Tomasz Moń <[email protected]>
(cherry picked from commit 152844a)

Author: tmon-nordic

subsys/usb/device_next/class/usbd_msc.c

@@ -718,6 +718,9 @@ static void usbd_msc_handle_request(struct usbd_class_data *c_data,
 		}
 	}
 	msc_free_scsi_buf(ctx, buf->__buf);
+	if (buf->frags) {
+		msc_free_scsi_buf(ctx, buf->frags->__buf);
+	}
 	usbd_ep_buf_free(uds_ctx, buf);
 }