drm/amdkfd: Copy wave state only for compute queue

get_wave_state is not defined for sdma queue, copy_context_work_handler
calls it for sdma queue will crash.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Jonathan Kim <jonathan.kim@amd.com>
Tested-by: Jonathan Kim <jonathan.kim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>