ASoC: Intel: sof_ssp_amp: always set dpcm_capture for amplifiers

The amplifier may provide hardware support for I/V feedback, or
alternatively the firmware may generate an echo reference attached to
the SSP and dailink used for the amplifier.

To avoid any issues with invalid/NULL substreams in the latter case,
always unconditionally set dpcm_capture.

Link: https://github.com/thesofproject/linux/issues/4083
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20230119163459.2235843-5-kai.vehmanen@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>