ASoC: SOF: Remove header from struct snd_sof_ipc_msg

ASoC: SOF: Remove header from struct snd_sof_ipc_msg

The header field is no longer used by the underlying code and
can be dropped from the snd_sof_ipc_msg struct.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20220330201926.1330402-11-ranjani.sridharan@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>