media: dvb_frontend: don't play tricks with underflow values

fepriv->auto_sub_step is unsigned. Setting it to -1 is just a
trick to avoid calling continue, as reported by Coverity.

It relies to have this code just afterwards:

	if (!ready) fepriv->auto_sub_step++;

Simplify the code by simply setting it to zero and use
continue to return to the while loop.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Author: mchehab

drivers/media/dvb-core/dvb_frontend.c

@@ -443,8 +443,8 @@ static int dvb_frontend_swzigzag_autotune(struct dvb_frontend *fe, int check_wra
 
 		default:
 			fepriv->auto_step++;
-			fepriv->auto_sub_step = -1; /* it'll be incremented to 0 in a moment */
-			break;
+			fepriv->auto_sub_step = 0;
+			continue;
 		}
 
 		if (!ready) fepriv->auto_sub_step++;