PM: wakeup: Remove unnecessary else from device_init_wakeup()

Checkpatch warns that else is generally not necessary after a return
condition which exists in the if part of this function.

Hence, just to abide by what checkpatch recommends, follow it's
guidelines.

Signed-off-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>