can: etas_es58x: fix potential NULL pointer dereference on udev->serial

In the Linux kernel, the following vulnerability has been resolved: can: etas_es58x: fix potential NULL pointer dereference on udev->serial The driver assumed that es58x_dev->udev->serial could never be NULL. While this is true on commercially available devices, an attacker could spoof the device identity providing a NULL USB serial number. That would trigger a NULL pointer dereference. Add a check on es58x_dev->udev->serial before accessing it.