SurfaceFlinger: set the refresh rate on overlay when calling to hwc

Change the refresh rate value on the overlay right after we set
the new refresh rate to hwc, instead of when we intend to change the
refresh rate. The latter may cause the display to freeze due to
a race condition where we intend to switch the refresh rate
and then abort (due to a infrequent layer update for example).

Bug: 183902142
Test: Swipe app to see app drawer and wait for the refresh rate to change
Change-Id: Id78efb96571b978d8adaabcff9aa30c32fe67786