PM: Update function header for dev_pm_get_subsys_data()

The commit "PM: Make dev_pm_get_subsys_data() always return 0 on success"
changed the return value from dev_pm_get_subsys_data(). Let's update the
comment in the function header to reflect this change as well.
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/common.c

@@ -19,8 +19,8 @@
  * @dev: Device to handle.
  *
  * If power.subsys_data is NULL, point it to a new object, otherwise increment
- * its reference counter.  Return 1 if a new object has been created, otherwise
- * return 0 or error code.
+ * its reference counter.  Return 0 if new object has been created or refcount
+ * increased, otherwise negative error code.
  */
 int dev_pm_get_subsys_data(struct device *dev)
 {