convert 'Stats stats; memset(&stats, 0, sizeof(Stats));' to 'Stats stats = {};'

Not only is it more concise, but it's also just a tad more correct:
since it really should have been 'sizeof(stats)' not 'sizeof(Stats)'.

Test: builds, atest
Bug: 146787904
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I6cf0295878c7b34cedfe3ae44ff7410ef419f8b9