drm/radeon: take the mode_config mutex when dealing with hpds (v2)

Since we are messing with state in the worker.

v2: drop the changes in the mst worker

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

diff --cc drivers/gpu/drm/radeon/radeon_irq_kms.c
Simple merge