ASoC: SOF: Intel: mtl: Do not process IPC reply before firmware boot

ASoC: SOF: Intel: mtl: Do not process IPC reply before firmware boot

It is not yet clear, but it is possible to create a firmware so broken
that it will send a reply message before a FW_READY message (it is not
yet clear if FW_READY will arrive later).
Since the reply_data is allocated only after the FW_READY message, this
will lead to a NULL pointer dereference if not filtered out.

Reported-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20220712122357.31282-4-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>