ALSA: trident: Drop shadow TLB pointer table

The shadow TLB pointer table is allocated and set up, but never really
used any longer by the driver.  Let's drop it.

Since this is the only user of snd_pcm_sgbuf_get_ptr(), we can clean
up the API after this change.

Link: https://lore.kernel.org/r/20210609162551.7842-2-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>