media: i2c: dw9768: remove unused struct 'regval_list'

'regval_list' is unused since the original
commit 85989122 ("media: i2c: dw9768: Add DW9768 VCM driver")

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>