PM / Runtime: Fix comments to match runtime callback code

Commit 05aa55dddb9ee4045c320661068bea78dad6a6e5 changed routines to
succeed if the driver handler is not defined. Comments were not updated.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
1 file changed