drm/amdgpu: fix transform feedback GDS hang on gfx10 (v2)

v2: update emit_ib_size
(though it's still wrong because it was wrong before)

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>