ALSA: trident: Remove always NULL parameters

The various PCM allocation functions in this driver take a pointer to a
pointer of a PCM where if this parameter is provided the newly allocated PCM
is stored. All callers pass NULL though, so remove the parameter.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>