drm/amdkfd: Delete a duplicate statement in set_pasid_vmid_mapping()

The same statement is later done in kgd_set_pasid_vmid_mapping(), so no
need to do it in set_pasid_vmid_mapping().

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>