V4L/DVB (7994): si470x: let si470x_get_freq return errno

This patch brings the following changes:
- version bumped to 1.0.8 for all the following patches
- si470x_get_freq now returns errno

Signed-off-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>