accel/rocket: clear rdev on device init failure

In the Linux kernel, the following vulnerability has been resolved: accel/rocket: clear rdev on device init failure rocket_probe() stores the return value from rocket_device_init() in the file-scoped rdev pointer before checking whether it is an error pointer. If rocket_device_init() fails, rdev is left as an ERR_PTR. The rdev pointer is also used as the marker for whether the shared rocket device has already been initialized. A later core probe can therefore see a non-NULL rdev, skip rocket_device_init(), and dereference the error pointer when reading rdev->num_cores. Save the error code and clear rdev before returning from the rocket_device_init() failure path.