drm/amdgpu: properly initialize return value during CS

The return value is no longer initialized before the loop because of
moving code around.

Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: c2b08e7a ("drm/amdgpu: move entity selection and job init earlier during CS")
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>