drm/amdgpu: Fix typo in amdgpu_vmid_mgr_init

fix a typo in for loop: i->j

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org