accel/rocket: search every core slot when a core is removed

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

accel/rocket: search every core slot when a core is removed

rocket_remove() decrements rdev->num_cores for each core it removes,
while find_core_for_dev() searches slots 0 to num_cores - 1. Unbinding
the cores in the order they were bound therefore loses the last one: by
the time it is removed the search range has already shrunk past its
slot, so find_core_for_dev() returns -1 and rocket_remove() gives up
without doing anything.

num_cores never reaches zero, rocket_device_fini() never runs, and the
file-scoped rdev keeps pointing at a device that is going away. Binding
the cores again starts from that stale count, because rocket_probe()
takes rdev->num_cores as the slot to fill. On an RK3588, which describes
three cores, the second round lands on slots 1, 2 and 3 while rdev->cores
was allocated with room for three:

rocket fdab0000.npu: Rockchip NPU core 1 version: 1179210309
rocket fdac0000.npu: Rockchip NPU core 2 version: 1179210309
rocket fdad0000.npu: Rockchip NPU core 3 version: 1179210309

The write to rdev->cores[3] is past the end of the array.

Nothing in tree reads the core array often enough to notice, so the
overrun is silent today. It turned up while testing a devfreq series on
top of this, where a worker walks every core a few times a second, and
UBSAN caught the first bool it read out of the overrun entry:

UBSAN: invalid-load in drivers/accel/rocket/rocket_devfreq.c:47:10
load of value 5 is not a valid value for type '_Bool'
Workqueue: devfreq_wq devfreq_monitor

Record how many slots were allocated and search all of them. Every core
is then found on removal, num_cores reaches zero, the device is torn down
and a later bind starts from a clean rdev.

This does not make unbinding a single core out of several work. probe
still takes num_cores as the slot to fill, so rebinding one core while
its siblings stay bound would write over a slot that is already in use,
and rocket_open() still reaches for cores[0] whether or not anything is
there. Both of those want more thought than a fix should carry.

Found by unbinding and rebinding all three cores on an Orange Pi 5 Plus.
With this applied, 25 unbind/rebind rounds and 5 module unload/reload
rounds run clean there: the cores land in slots 0, 1 and 2 every time,
whichever order they are bound in, and the shared supply goes back to a
single user after each round.