drm/amdgpu: fix the broken vm->mutex V2

fix the vm->mutex and ww_mutex confilcts.
vm->mutex is always token first, then ww_mutex.

V2: remove unneccessary checking for pt bo.

Change-Id: Iea56e183752c02831126d06d2f5b7a474a6e4743
Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>