drm/amdgpu/gmc9: print client id string for gfxhub

Print the name of the client rather than the number.  This
makes it easier to debug what block is causing the fault.

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>