V4L/DVB (6893): tuner-xc2028: fix xc2028_attach function

xc2028_attach was returning an integer when disabled from the build, where it
should instead be returning NULL.  Declare xc2028_attach as type dvb_frontend *
instead of void *.

The prototype declaration must be marked as extern in the header.
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/tuner-xc2028.c

@@ -1140,7 +1140,8 @@ static const struct dvb_tuner_ops xc2028_dvb_tuner_ops = {
 
 };
 
-void *xc2028_attach(struct dvb_frontend *fe, struct xc2028_config *cfg)
+struct dvb_frontend *xc2028_attach(struct dvb_frontend *fe,
+				   struct xc2028_config *cfg)
 {
 	struct xc2028_data *priv;
 	void               *video_dev;

drivers/media/video/tuner-xc2028.h

@@ -48,14 +48,15 @@ struct xc2028_config {
 #define XC2028_RESET_CLK	1
 
 #if defined(CONFIG_TUNER_XC2028) || (defined(CONFIG_TUNER_XC2028_MODULE) && defined(MODULE))
-void *xc2028_attach(struct dvb_frontend *fe, struct xc2028_config *cfg);
+extern struct dvb_frontend *xc2028_attach(struct dvb_frontend *fe,
+					  struct xc2028_config *cfg);
 #else
-void *xc2028_attach(struct dvb_frontend *fe,
-				struct xc2028_config *cfg)
+static inline struct dvb_frontend *xc2028_attach(struct dvb_frontend *fe,
+						 struct xc2028_config *cfg)
 {
 	printk(KERN_INFO "%s: not probed - driver disabled by Kconfig\n",
 	       __FUNCTION__);
-	return -EINVAL;
+	return NULL;
 }
 #endif