amdgpu/dc: Fix double unlock in amdgpu_dm_commit_planes

Reported by smartch:
amdgpu_dm_commit_planes() error: double unlock 'spin_lock:&crtc->dev->event_lock'
amdgpu_dm_commit_planes() error: double unlock 'irqsave:flags'

The error path doesn't return so we only need a single unlock.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Ernst Sjöstrand <ernstp@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -3904,7 +3904,6 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 			DRM_ERROR("%s: acrtc %d, already busy\n",
 				  __func__,
 				  acrtc_attach->crtc_id);
-			spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
 			/* In commit tail framework this cannot happen */
 			WARN_ON(1);
 		}