accel/rocket: fix unwinding in error path in rocket_probe

In the Linux kernel, the following vulnerability has been resolved:

accel/rocket: fix unwinding in error path in rocket_probe

When rocket_core_init() fails (as could be the case with EPROBE_DEFER), we need to properly unwind by decrementing the counter we just incremented and if this is the first core we failed to probe, remove the rocket DRM device with rocket_device_fini() as well. This matches the logic in rocket_remove(). Failing to properly unwind results in out-of-bounds accesses.