drm/vmwgfx: Invalidate surface on non-readback unbind

Fixes error messages in vmware.log

Signed-off-by: Jakob Bornecrantz <jakob@vmware.com>
Reviewed-by: Michael Banack <banackm@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

diff --cc drivers/gpu/drm/vmwgfx/vmwgfx_surface.c
Simple merge