ASoC: hdac_hdmi: avoid reference to invalid variable of the pin list

Using pin list array iterator outside the iteration of the list can
point to dummy element, which can be invalid. So don't use pin variable
outside the pin list iteration.

This fixes the following coccinelle warning:
sound/soc/codecs/hdac_hdmi.c:1419:5-8: ERROR: invalid reference to the
index variable of the iterator

Fixes: 2acd8309('ASoC: hdac_hdmi: Add support to handle MST capable pin')
Reported-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Jeeja KP <jeeja.kp@intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>