drm/vc4: kms: Add missing drm_crtc_commit_put

Commit 9ec03d7f ("drm/vc4: kms: Wait on previous FIFO users before a
commit") introduced a global state for the HVS, with each FIFO storing
the current CRTC commit so that we can properly synchronize commits.

However, the refcounting was off and we thus ended up leaking the
drm_crtc_commit structure every commit. Add a drm_crtc_commit_put to
prevent the leakage.

Fixes: 9ec03d7f ("drm/vc4: kms: Wait on previous FIFO users before a commit")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Tested-by: Jian-Hong Pan <jhp@endlessos.org>
Link: https://lore.kernel.org/r/20211117094527.146275-4-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -361,6 +361,7 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 		struct vc4_crtc_state *vc4_crtc_state =
 			to_vc4_crtc_state(old_crtc_state);
 		unsigned int channel = vc4_crtc_state->assigned_channel;
+		struct drm_crtc_commit *commit;
 		int ret;
 
 		if (channel == VC4_HVS_CHANNEL_DISABLED)
@@ -369,9 +370,15 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 		if (!old_hvs_state->fifo_state[channel].in_use)
 			continue;
 
-		ret = drm_crtc_commit_wait(old_hvs_state->fifo_state[channel].pending_commit);
+		commit = old_hvs_state->fifo_state[channel].pending_commit;
+		if (!commit)
+			continue;
+
+		ret = drm_crtc_commit_wait(commit);
 		if (ret)
 			drm_err(dev, "Timed out waiting for commit\n");
+
+		drm_crtc_commit_put(commit);
 	}
 
 	if (vc4->hvs->hvs5)