Migrate to onViewCreated in DataSaverSummary

The onActivityCreated method has been deprecated. This change updates
DataSaverSummary to use onViewCreated instead, which is the recommended
method for initializing views after the fragment's view has been created.

Test: manual
Change-Id: I08daa11b557b05441fa4f7ed0019802d991846e3
Signed-off-by: Jyotiraditya Panda <jyotiraditya@aospa.co>