mailbox: mtk-adsp: fix UAF during device teardown

mailbox: mtk-adsp: fix UAF during device teardown

When the SOF audio driver fails to initialize (e.g. firmware boot
timeout), its devres unwind frees the snd_sof_dev object that the
mailbox client (mtk-adsp-ipc) reaches via chan->cl->rx_callback.
The mtk-adsp-mailbox shutdown clears the mailbox command registers
but leaves the IRQ line unmasked, so a late interrupt can still
queue a threaded handler after mbox_free_channel() had cleared
chan->cl, and mbox_chan_received_data() would then trigger UAF:

  BUG: KASAN: slab-use-after-free in sof_ipc3_validate_fw_version
   sof_ipc3_validate_fw_version
   sof_ipc3_do_rx_work
   sof_ipc3_rx_msg
   mt8196_dsp_handle_request
   mtk_adsp_ipc_recv
   mbox_chan_received_data
   mtk_adsp_mbox_isr
   irq_thread_fn
  Freed by task ...:
   kfree
   devres_release_all
   really_probe
   ... (sof-audio-of-mt8196 probe failure)

The crash was observed roughly three seconds after the failed probe.

disable_irq() in shutdown and enable_irq() in startup. disable_irq()
also waits for any in-flight interrupts, so by the time
mbox_free_channel() proceeds to clear chan->cl no rx_callback can run.

In addition, request the IRQ with IRQF_NO_AUTOEN so it stays masked
between probe and the first client bind — otherwise an early interrupt
can crash on chan->cl == NULL in mbox_chan_received_data().

Fixes: af2dfa96c52d ("mailbox: mediatek: add support for adsp mailbox controller")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>