drm/amdgpu: workaround for TLB seq race

commit 77c092e0

 upstream.

It can happen that we query the sequence value before the callback
had a chance to run.

Workaround that by grabbing the fence lock and releasing it again.
Should be replaced by hw handling soon.

Signed-off-by: Christian König <christian.koenig@amd.com>
CC: stable@vger.kernel.org # 5.19+
Fixes: 5255e146

 ("drm/amdgpu: rework TLB flushing")
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2113
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Philip Yang <Philip.Yang@amd.com>
Tested-by: Stefan Springer <stefanspr94@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>