ASoC: pcm: Do not open FEs with no BEs connected

ASoC: pcm: Do not open FEs with no BEs connected

The check is performed in prepare-step, that is dpcm_fe_dai_prepare()
but that is very late - code operates on invalid configuration from
dpcm_fe_dai_open() till it gets there. Relocate the check to the
open-step to avoid any invalid scenarios.

Reviewed-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://patch.msgid.link/20250530141231.2943351-1-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>