ASoC: soc-core: clear platform pointers on error

Originally snd_soc_init_platform was not cleaning up its pointers, this
was fixed to always reallocate dynamic memory but created a memory leak
when snd_soc_init_platform was called multiple times during the same
probe attempt and also threw away any changes made to the struct between
calls. In order to avoid reallocating memory that is still valid, the
behaviour will be changed to clear the dynamically set pointers on a
probe error and a unregister event and snd_soc_init_platform will go
back to its original behaviour of only allocating null pointers so it will
stop throwing away valid changes.

Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>