V4L/DVB (3420): Nskips maybe used uninitialized in bttv_risc_overlay

The Coverity checker (previously Stanford checker) noticed that
the value of nskips could be read even if it was never written.
Signed-off-by: Duncan Sands <baldrick@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/bttv-risc.c

@@ -276,6 +276,8 @@ bttv_risc_overlay(struct bttv *btv, struct btcx_riscmem *risc,
 		if (line > maxy)
 			btcx_calc_skips(line, ov->w.width, &maxy,
 					skips, &nskips, ov->clips, ov->nclips);
+		else
+			nskips = 0;
 
 		/* write out risc code */
 		for (start = 0, skip = 0; start < ov->w.width; start = end) {