Hibernation: Fix comment in disk.c

Fix a comment in kernel/power/disk.c so that it doesn't contain lines
longer that 80 characters.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Len Brown <len.brown@intel.com>