ASoC: hdac_hdmi: Fix to warn instead of err for no connected nids

It is possible that some pin widget may return with no converter
connected. So don't throw error if none are found to be connected.
Instead print a warning and continue.

Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>