CVE-2021-47534

In the Linux kernel, the following vulnerability has been resolved:
drm/vc4: kms: Add missing drm_crtc_commit_put Commit 9ec03d7f1ed3
(“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.