AudioFlinger: do not reset mHwPaused on flush

The hardware pause feature is hidden from the track clients.
Make the current implementation consistent that when mHwPaused
is set it requires a resume() after a flush().

Test: see bug
Bug: 335784313
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:88f1dd08f127ca918a261428aac7928defa156c3)
Merged-In: I4c7db89277a6144b9b78223fa6f899c85adfb3fc
Change-Id: I4c7db89277a6144b9b78223fa6f899c85adfb3fc