Use Kotlin member naming convention consistently

NotificationWakeUpCoordinator had a weird mix of the member naming
conventions for Java (mSomeMemberName) and Kotlin (someMemberName).

This is confusing -- they make me wonder if they're variables from a
superclass -- and distracting while reading code, and they're only used
within that single file, so rename them all.

Bug: 347731926
Test: mechanical rename, so just build and presubmit
Flag: EXEMPT mechanical rename, no code change
Change-Id: I5b99aca45d6b07f746e8c5cb39b8fc5c2c69ac07