V4L/DVB (3568e): bt856: Spare memory

The bt856 driver has a register cache much larger than needed.  We really only
write to 3 registers, so a 32-byte cache is a bit too much.  We can be just as
efficient with a 6-byte cache.  We could even do with a 3-byte cache, but at
the cost of additional arithmetics arguably not worth the spared 3 bytes.

Also, 4 of the 6 other members of the bt856 data structure were not used
anywhere, so we can as well drop them for an additional 16 bytes of memory
spared.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>