drm/radeon: invalidate moved BOs in the VM (v2)

Don't wait for the BO to be used again, just
update the PT on the next VM use.

v2: remove stray semicolon.

Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>