V4L/DVB (9631): Make s2api work for ATSC support

ATSC should be considered a legacy delivery system, or else fields such as
p->u.vsb.modulation do not get populated (resulting in set_frontend failures)

Cc: Steven Toth <[e-mail]>
Signed-off-by: Devin Heitmueller <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/dvb/dvb-core/dvb_frontend.c

···
 int is_legacy_delivery_system(fe_delivery_system_t s)
 {
 	if((s == SYS_UNDEFINED) || (s == SYS_DVBC_ANNEX_AC) ||
-		(s == SYS_DVBC_ANNEX_B) || (s == SYS_DVBT) || (s == SYS_DVBS))
+	   (s == SYS_DVBC_ANNEX_B) || (s == SYS_DVBT) || (s == SYS_DVBS) ||
+	   (s == SYS_ATSC))
 		return 1;
 
 	return 0;