[media] siano: make some functions static

drivers/media/common/siano/smsdvb-debugfs.c:51:6: warning: no previous prototype for 'smsdvb_print_dvb_stats' [-Wmissing-prototypes]
drivers/media/common/siano/smsdvb-debugfs.c:154:6: warning: no previous prototype for 'smsdvb_print_isdb_stats' [-Wmissing-prototypes]
drivers/media/common/siano/smsdvb-debugfs.c:244:6: warning: no previous prototype for 'smsdvb_print_isdb_stats_ex' [-Wmissing-prototypes]
drivers/media/common/siano/smscoreapi.c:832:5: warning: no previous prototype for 'smscore_configure_board' [-Wmissing-prototypes]
drivers/media/common/siano/smscoreapi.c:1301:5: warning: no previous prototype for 'smscore_init_device' [-Wmissing-prototypes]

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>