ASoC: wm_adsp: For TLV controls only register TLV get/set

Normal 512-byte get/set of a TLV isn't supported but we were
registering the normal get/set anyway and relying on omitting
the SNDRV_CTL_ELEM_ACCESS_[READ|WRITE] flags to prevent them
being called.

Trouble is if this gets broken in the core ALSA code - as it has
been since at least 4.14 - the standard get/set can be called
unexpectedly and corrupt memory.

There's no point providing functions that won't be called and
it's a trivial change. The benefit is that if the ALSA core gets
broken again we get a big fat immediate NULL dereference instead
of a memory corruption timebomb.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org