V4L/DVB: stv0900: make local functions static

V4L/DVB: stv0900: make local functions static

The functions stv0900_sw_algo() and stv0900_set_dvbs1_track_car_loop() are only used
locally so mark them static.

This will remove the following sparse warnings (see "make C=1"):
 * symbol 'stv0900_sw_algo' was not declared. Should it be static?
 * symbol 'stv0900_set_dvbs1_track_car_loop' was not declared. Should it be static?

Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>