[media] bttv: stop abusing mbox_we for sw_status

Kodicom 4400R and Geovision GV-800 code in bttv driver abuses mbox_we (int)
in struct bttv as char *.
Remove this hack and add a proper sw_status array to struct bttv instead.
This is a a preparation to remove mbox_we.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>