drm/amdkfd: page_table_base already have the flags needed

The flags are added when calling amdgpu_gmc_pd_addr().

Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>