[media] dib7000p: fix sparse warning

drivers/media/dvb-frontends/dib7000p.c:2562:5: warning: symbol 'dib7090_set_diversity_in' was not declared. Should it be static?

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>