media: go7007: Constify static struct snd_device_ops

The only usage of go7007_snd_device_ops is to pass its address to
snd_device_new() which takes a pointer to const struct snd_device_ops.
Make it const to allow the compiler to put it in read-only memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>