ASoC: SOF: Intel: pci-mtl: fix firmware name

ASoC: SOF: Intel: pci-mtl: fix firmware name

Initial IPC4 tests used the same conventions as previous reference
closed-source firmware, but for MeteorLake the convention is the same
as previous SOF releases (sof-<platform>.ri). Only the prefix changes
to avoid confusions between IPC types.

This change has no impact on users since the firmware has not yet been
released.

Fixes: 064520e8aeaa2 ("ASoC: SOF: Intel: Add support for MeteorLake (MTL)")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Chao Song <chao.song@intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20221017204004.207446-1-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>