drm/amdgpu: catch amdgpu_irq_add_id failure

Do not ignore amdgpu_irq_add_id return value while registering
VMC page fault interrupt.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>