drm/gem: free vma-node during object-cleanup

All drivers currently need to clean up the vma-node manually. There is no
fancy logic involved so lets just clean it up unconditionally. The
vma-manager correctly catches multiple calls so we are fine.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

diff --cc drivers/gpu/drm/drm_gem.c
Simple merge