ASoC: wm_adsp: Fix NULL dereference when removing firmware controls

ASoC: wm_adsp: Fix NULL dereference when removing firmware controls

In wm_adsp_control_remove() check that the priv pointer is not NULL
before attempting to cleanup what it points to.

When cs_dsp creates a control it calls wm_adsp_control_add_cb() so that
wm_adsp can create its own private control data. There are two cases
where private data is not created:

1. The control is a SYSTEM control, so an ALSA control is not created.

2. The codec driver has registered a control_add() callback that
   hides the control, so wm_adsp_control_add() is not called.

When cs_dsp_remove destroys its control list it calls
wm_adsp_control_remove() for each control. But wm_adsp_control_remove()
was attempting to cleanup the private data pointed to by cs_ctl->priv
without checking the pointer for NULL.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 0700bc2fb94c ("ASoC: wm_adsp: Separate generic cs_dsp_coeff_ctl handling")
Link: https://patch.msgid.link/20260604101244.1402862-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>