camera2: Improve code readability for FrameNumberTracker.

Bug: 168713666

Test: builds
Test: GCA (basic validity)

Change-Id: Id0f9b5a9a6363f40daa9384ee5f01b47d36ad139
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>
(cherry picked from commit 91f7bc0b3b1605c46b64ecf41ede357192df39df)
1 file changed