V4L/DVB (6246): GemTek Radio card - Control Word

Redoes the way the control word is stored and set.
The existing code was a lot more complicated than it needed to be.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Douglas Schilling Landgraf <dougsland@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Reviewed-by: Pekka Seppänen <pexu@kapsi.fi>