dvb-frontends: use IS_REACHABLE() instead of IS_ENABLED()

Changeset 9b174527 added this new macro, ensuring that it
is true only if the function is actually reachable.

However, newer drivers were added since when it was written.
So, change those drivers to also use it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/dvb-frontends/drx39xyj/drx39xxj.h

@@ -34,7 +34,7 @@ struct drx39xxj_state {
 	const struct firmware *fw;
 };
 
-#if IS_ENABLED(CONFIG_DVB_DRX39XYJ)
+#if IS_REACHABLE(CONFIG_DVB_DRX39XYJ)
 struct dvb_frontend *drx39xxj_attach(struct i2c_adapter *i2c);
 #else
 static inline struct dvb_frontend *drx39xxj_attach(struct i2c_adapter *i2c) {

drivers/media/dvb-frontends/lgdt3306a.h

@@ -58,7 +58,7 @@ struct lgdt3306a_config {
 	int  xtalMHz;
 };
 
-#if IS_ENABLED(CONFIG_DVB_LGDT3306A)
+#if IS_REACHABLE(CONFIG_DVB_LGDT3306A)
 struct dvb_frontend *lgdt3306a_attach(const struct lgdt3306a_config *config,
 				      struct i2c_adapter *i2c_adap);
 #else

drivers/media/dvb-frontends/si2165.h

@@ -45,7 +45,7 @@ struct si2165_config {
 	bool inversion;
 };
 
-#if IS_ENABLED(CONFIG_DVB_SI2165)
+#if IS_REACHABLE(CONFIG_DVB_SI2165)
 struct dvb_frontend *si2165_attach(
 	const struct si2165_config *config,
 	struct i2c_adapter *i2c);