drm/amdgpu: Update the impelmentation of AMDGPU_PTE_MTYPE_VG10

This patch changes the implementation of AMDGPU_PTE_MTYPE_VG10,
clear the bits before setting the new one.

Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: longlyao <Longlong.Yao@amd.com>
Signed-off-by: Shane Xiao <shane.xiao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>