drm/radeon/kms/vm: fix possible bug in radeon_vm_bo_rmv()

The bo is removed from the list at the top of
radeon_vm_bo_rmv(), but then the list is used
in radeon_vm_bo_update_pte() to look up the vm.
remove the bo_list entry at the end of the
function instead.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jerome Glisse <j.glisse@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>