drivers/base/power/opp.c: fix dev_opp initial value

Dev_opp initial value shoule be ERR_PTR(), IS_ERR() is used to check
error.

Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/power/opp.c

@@ -453,7 +453,7 @@ int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
 static int opp_set_availability(struct device *dev, unsigned long freq,
 		bool availability_req)
 {
-	struct device_opp *tmp_dev_opp, *dev_opp = NULL;
+	struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
 	struct opp *new_opp, *tmp_opp, *opp = ERR_PTR(-ENODEV);
 	int r = 0;