[media] radio-si476x: add return value check to avoid dead code

Dead code found on below code:
    si476x_radio_add_new_custom(radio, SI476X_IDX_DIVERSITY_MODE);
    if (rval < 0)
            goto exit;

    si476x_radio_add_new_custom(radio, SI476X_IDX_INTERCHIP_LINK);
    if (rval < 0)  ====> Dead code !!!
            goto exit;

The piece of code miss return value check after calling .si476x_radio_add_new_custom(),
the patch fix it.
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/radio/radio-si476x.c

@@ -1530,11 +1530,11 @@ static int si476x_radio_probe(struct platform_device *pdev)
 	if (si476x_core_has_diversity(radio->core)) {
 		si476x_ctrls[SI476X_IDX_DIVERSITY_MODE].def =
 			si476x_phase_diversity_mode_to_idx(radio->core->diversity_mode);
-		si476x_radio_add_new_custom(radio, SI476X_IDX_DIVERSITY_MODE);
+		rval = si476x_radio_add_new_custom(radio, SI476X_IDX_DIVERSITY_MODE);
 		if (rval < 0)
 			goto exit;
 
-		si476x_radio_add_new_custom(radio, SI476X_IDX_INTERCHIP_LINK);
+		rval = si476x_radio_add_new_custom(radio, SI476X_IDX_INTERCHIP_LINK);
 		if (rval < 0)
 			goto exit;
 	}