media: ddbridge: fix gap handling

Force gap setting if given by attribute and enable gap for older regmaps.
Also, setting a gap value of 128 via sysfs will now disable gap.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>