PM: Make dev_pm_get_subsys_data() always return 0 on success

Commits 1d5fcfec22 (PM / Domains: Add device domain data reference
counter) and 62d4490294 (PM / Domains: Allow device callbacks to be
added at any time) added checks for the return value of
dev_pm_get_subsys_data(), but those checks were incorrect, because
that function returned 1 on success in some cases.

Since all of the existing users of dev_pm_get_subsys_data() don't use
the positive value returned by it on success, change its definition
so that it always returns 0 when successful.

Reported-by: Heiko Stübner <heiko@sntech.de>
Reported-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
index 869d7ff..eb78e96 100644
--- a/drivers/base/power/clock_ops.c
+++ b/drivers/base/power/clock_ops.c
@@ -169,8 +169,7 @@
  */
 int pm_clk_create(struct device *dev)
 {
-	int ret = dev_pm_get_subsys_data(dev);
-	return ret < 0 ? ret : 0;
+	return dev_pm_get_subsys_data(dev);
 }
 
 /**