drm/amdkfd: Don't acquire buffers during CRIU queue restore.

drm/amdkfd: Don't acquire buffers during CRIU queue restore.

kfd_criu_restore_queue's call of kfd_queue_acquire_buffers was
failing for multiple reasons
- The ctl_stack_size set by the CRIU plugin doesn't match
what is expected by acquire_buffers
- The svm buffer cannot be acquired at this point because
CRIU may not have restored it, or may have restored it
to a different address.

The only reason acquire_buffers was necessary here was to
avoid a null ptr dereference in init_user_queue.

Just put in a check for that dereference; it doesn't appear to
come up in real use cases right now. That is, there is no
usage of CRIU with shared MES.

This is a partial revert of
commit 20a5e7ffdfec ("drm/amdkfd: Properly acquire queue buffers in CRIU restore")

Fixes: 20a5e7ffdfec ("drm/amdkfd: Properly acquire queue buffers in CRIU restore")
Reviewed-by: David Yat Sin <david.yatsin@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 1cafa8b29e029eac3ddf64604f891b35dbf6262b)
Cc: stable@vger.kernel.org