mmc: vub300: fix use-after-free on probe failure

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

mmc: vub300: fix use-after-free on probe failure

The vub300 driver lifetime-manages its controller state using
vub300->kref, with vub300_delete() freeing the mmc host when the last
reference is dropped. The probe error path after the inactivity timer has
been armed still bypasses that lifetime rule, however, and falls through
to mmc_free_host() directly if mmc_add_host() fails.

The race window is between arming the inactivity timer and reaching the
probe error unwind after mmc_add_host() fails:

probe thread timer/workqueue
------------ ---------------
kref_init(&vub300->kref) ref = 1
kref_get(&vub300->kref) ref = 2, timer ref
add_timer(inactivity_timer) fires after one second
|
| race window
|<---------------------------------------------------->
|
mmc_add_host(mmc)
inactivity timer fires
vub300_queue_dead_work()
kref_get() ref = 3
queue_work(deadwork)
mmc_add_host() fails
timer_delete_sync()
mmc_free_host(mmc)
frees vub300
deadwork runs
use-after-free

The inactivity timeout is one second, so this would require
mmc_add_host() to both fail and take more than one second to do so. This
is unlikely to happen in practice, but the error path is still wrong.

timer_delete_sync() only waits for the timer callback itself. It does
not flush deadwork that the callback may already have queued. As a
result, queued deadwork can still hold a kref while the probe error path
directly frees the backing mmc host, including the vub300 storage.

Fix this by using the same lifetime mechanism as disconnect. Clear
vub300->interface so that the timer callback and any queued deadwork
return early and drop their references, then drop the initial probe
reference and return without falling through to err_free_host.