Fix this compile warning:

v4l/dvb-bt8xx.c: In function 'cx24108_tuner_set_params':
v4l/dvb-bt8xx.c:221: warning: array subscript is above array bounds

Make sure that we never get past the last element in the array.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>