V4L/DVB (7375): cx88/saa7134: fix magic number for xc3028 reusage detection

tuner-xc2028 needs to know when a DVB module is sharing the same analog tuner.
This is done by comparing a magic number that needs to be the same on analog
and on digital. To make easier, this magic number is a pointer to some data
struct.

With the previous code, two different pointers were using, causing a
miss-detection.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>