drm_hwcomposer: Fix invalid buffer_handle_t pointer

Always update the buffer_handle_t pointer in setLayerBuffer regardless
of composition type rather than keeping the invalid buffer_handle_t in
the Layer obect. The composition type may be changed back to device
composition by setLayerCompositionType at which point the Layer object
needs to have saved the buffer_handle_t.

Signed-off-by: Paul Howgego <paul.howgego@arm.com>
1 job for fix-setlayerbuffer in 39 seconds (queued for 2 seconds)