drm/amdgpu/sdma6: properly reference trap interrupts for userqs

We need to take a reference to the interrupts to make
sure they stay enabled even if the kernel queues have
disabled them.

Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>