[media] cx22700: Fix potential buffer overflow

As new FEC types were added, we need a check to avoid overflows:
	drivers/media/dvb-frontends/cx22700.c:172 cx22700_set_tps() error: buffer overflow 'fec_tab' 6 <= 6
	drivers/media/dvb-frontends/cx22700.c:173 cx22700_set_tps() error: buffer overflow 'fec_tab' 6 <= 6

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/dvb-frontends/cx22700.c

@@ -169,6 +169,9 @@ static int cx22700_set_tps(struct cx22700_state *state,
 
 	cx22700_writereg (state, 0x04, val);
 
+	if (p->code_rate_HP - FEC_1_2 >= sizeof(fec_tab) ||
+	    p->code_rate_LP - FEC_1_2 >= sizeof(fec_tab))
+		return -EINVAL;
 	val = fec_tab[p->code_rate_HP - FEC_1_2] << 3;
 	val |= fec_tab[p->code_rate_LP - FEC_1_2];