drm/amdgpu: Fix kdoc style in amdgpu_fence.c

drm/amdgpu: Fix kdoc style in amdgpu_fence.c

The initial comment block before
amdgpu_fence_driver_guilty_force_completion() incorrectly used '/**' but
is not a kernel-doc comment, causing build warnings.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c:742: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Kernel queue reset handling

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>