[media] dvb_frontend: fix a regression with DVB-S zig-zag

Changeset 5bfaadde broke zig-zag for DVB-S drivers that don't
implement get_tune_settings() callback.

Fix the code, in order to allow it to work as before, otherwise
some channels may not be tuned anymore.

Fix Fedora Bugzilla:
	https://bugzilla.redhat.com/show_bug.cgi?id=814404

Cc: stable@kernel.org # for Kernel v3.3
Reported-by: NMichael Heijenga <database.worker@googlemail.com>
Tested-by: NMichael Heijenga <database.worker@googlemail.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

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

@@ -1921,6 +1921,10 @@ static int dtv_set_frontend(struct dvb_frontend *fe)
 	} else {
 		/* default values */
 		switch (c->delivery_system) {
+		case SYS_DVBS:
+		case SYS_DVBS2:
+		case SYS_ISDBS:
+		case SYS_TURBO:
 		case SYS_DVBC_ANNEX_A:
 		case SYS_DVBC_ANNEX_C:
 			fepriv->min_delay = HZ / 20;