drm/amdgpu: Remove unnecessary domain argument

Remove the "domain" argument to amdgpu_bo_create_kernel_at() since this
function takes an "offset" argument which is the offset off of VRAM, and as
such allocation always takes place in VRAM. Thus, the "domain" argument is
unnecessary.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: AMD Graphics <amd-gfx@lists.freedesktop.org>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>