drm/amdgpu: correct the name of mes_pipe structure

Correct the structure name admgpu_mes_pipe to amdgpu_mes_pipe.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Mukul Joshi <mukul.joshi@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>