drm/amdgpu/sdma: fix typo in packet setup

Use the correct define.  No functional change as both
defines are equivalent.

Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>