ASoC: Intel: avs: Fix avs_path_module::instance_id size

ASoC: Intel: avs: Fix avs_path_module::instance_id size

All IPCs using instance_id use 8 bit value. Original commit used 16 bit
value because FW reports possible max value in 16 bit field, but in
practice FW limits the value to 8 bits.

Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Link: https://lore.kernel.org/r/20230519201711.4073845-7-amadeuszx.slawinski@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>