ALSA: es1688: Drop superfluous ioctl PCM ops

snd_es1688_ioctl() does nothing but calling the default handler.
Now PCM core accepts NULL as the default ioctl ops(*), so let's drop
altogether.

(*) commit fc033cbf ("ALSA: pcm: Allow NULL ioctl ops")

Link: https://lore.kernel.org/r/20191210061145.24641-7-tiwai@suse.de


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