drm/amdgpu: fix doorbell regression

This patch adds a missed handling of PL domain doorbell while
handling VRAM faults.

Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Fixes: a6ff969f ("drm/amdgpu: fix visible VRAM handling during faults")
Reviewed-by: Christian Koenig <christian.koenig@amd.com>
Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Arvind Yadav <arvind.yadav@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>