drm/amdkfd: Walk through list with dqm lock hold

[ Upstream commit 56f221b6389e7ab99c30bbf01c71998ae92fc584 ]

To avoid any list corruption.

Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>