V4L/DVB (4592): Fixes some troubles on saa7115

Scaling were not working fine;
Some reserved registers were wrong;
On some situations, saa7115 were not properly being initializated.
Removed some duplicated code.
Thanks-to: Hans Verkuil <hverkuil@xs4all.nl> for co-working on this
patch.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>