ASoC: wcd9320: Add NULL check to avoid crash

Check for NULL pointer before passing the parameter for string
manipulation to avoid pointer dereference.

Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
ASoC: wcd9xxx: Don't enable micbias if headset is removed

If special headset is removed, the callback to
disable micbias will be called, as micbias is
always on with special headset. Mbhc driver
checks a flag, used to disable/enable micbias
for special headset, to make sure micbias is
not disabled by recording. If this flag is not
updated properly before the callback is called
while the headset is removed, it can cause that
micbias is left enabled.

Signed-off-by: Simmi Pateriya <simmip@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>