ASoC: dapm: Avoid uninitialised variable warning

Commit 4a75aae1 ("ASoC: dapm: Add support for multi-CODEC
CODEC to CODEC links") adds loops that iterate over multiple
CODECs in snd_soc_dai_link_event. This also introduced a compiler
warning for a potentially uninitialised variable in the case
no CODECs are present. This should never be the case as the
DAI link must by definition contain at least 1 CODEC however
probably best to avoid the compiler warning by initialising ret
to zero.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>