Make smart idle maint update write amount record every period

Now, when the condition doesn't meet, smart idle maintenance service
doesn't update write amount record. Fixed it, since it should be updated
every period.

Test: check smart idle maint log of StorageManagerService
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Change-Id: I339109fcaa821620a3b9b4b8c49e25fd18d03cf3