media: i2c: tw9910: remove unused strust 'regval_list'

'regval_list' has been unused since
commit 398994c1 ("V4L/DVB (13666): tw9910: modify V/H outpit pin
setting to use VALID").

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>