PM / hibernate: Change message when writing to /sys/power/resume

This file is used both for setting the wakeup device without kernel
command line as well as for actually waking the system (when appropriate
swap header is in place).

To avoid confusion on incorrect logs in system log downgrade the
message to debug and make it clearer.

Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>