PM: Simplify suspend_device

Reduce code duplication in drivers/base/suspend.c by introducing a separate
function for printing diagnostic messages.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>