ASoC: core: Don't defer probe on optional, NULL components

cpu and platform are optional components in DAI links. For example
codec-codec links usually have no platform set.

Call snd_soc_find_component only if the name or of_node of
a cpu or platform is set. Otherwise it will return NULL and
soc_init_dai_link bails out immediately with -EPROBE_DEFER,
meaning registering a card with NULL cpu or platform in DAI links
can never succeed.

Fixes: 8780cf11 ("ASoC: soc-core: defer card probe until all component is added to list")

Signed-off-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>