drm/amdkfd: Use S_ENDPGM_SAVED in trap handler

This instruction has no functional difference to S_ENDPGM
but allows performance counters to track save events correctly.

Signed-off-by: Jay Cornwall <jay.cornwall@amd.com>
Reviewed-by: Laurent Morichetti <laurent.morichetti@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>