drm/amd/display: add missing tracepoint event in DM atomic_commit_tail

There are two events to trace the beginning and the end of
amdgpu_dm_atomic_commit_tail, but only the one ate the beginning was
placed. Place amdgpu_dm_atomic_commit_tail_finish tracepoint at the end
than.

Signed-off-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>