V4L/DVB (5472): Isl6421: don't reference freed memory

After freeing a block there should be no reference to this block.

Signed-off-by: Thomas Viehweger <Thomas.Viehweger@marconi.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
diff --git a/drivers/media/dvb/frontends/isl6421.c b/drivers/media/dvb/frontends/isl6421.c
index ef31936..c967148 100644
--- a/drivers/media/dvb/frontends/isl6421.c
+++ b/drivers/media/dvb/frontends/isl6421.c
@@ -122,6 +122,7 @@
 	/* detect if it is present or not */
 	if (isl6421_set_voltage(fe, SEC_VOLTAGE_OFF)) {
 		kfree(isl6421);
+		fe->sec_priv = NULL;
 		return NULL;
 	}