V4L/DVB (3568b): saa7111: Prevent array overrun

Explicitely state the number of registers the SAA7111 has, and use that
defined value where relevant.  This should prevent any future array overrun
like the one I just fixed in the saa7110 driver.

This patch also saves 8 bytes of memory as a side effect, as the register
cache was larger than needed.

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>