drm/msm: dpu: Fix memory leak caused by dropped reference

We are currently leaking a drm_crtc_commit struct for every atomic
commit containing plane state. The dpu plane destroy function cleans up
the fb reference manually, but fails to release the commit ref. As a
result, we just keep allocating drm_crtc_commits without ever freeing
them. Fortunately there's a helper function which will clean up all of
our mess at once, so use that.

Thanks to Doug Anderson for reporting the memory leak (and leaving
breadcrumbs from kmemleak!).

Reported-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>