Use mDrawingState for printing hwc layers

mCurrentState does not show mirror layers, so the the --hwclayers
section was showing no layers on a display that simply contains mirror
layers. Use mDrawingState, which does, so that all layers are dumped.

Fixes: 248568076
Test: dumpsys SurfaceFlinger
Change-Id: Ia82490e5d8b213cd248ef6f0a9838cbe4b75919b