[media] sp2: sp2_init() can be static

drivers/media/dvb-frontends/sp2.c:269:5: sparse: symbol 'sp2_init' was not declared. Should it be static?
drivers/media/dvb-frontends/sp2.c:351:5: sparse: symbol 'sp2_exit' was not declared. Should it be static?

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>