drm/msm: fix use-after-free on probe deferral

In the Linux kernel, the following vulnerability has been resolved:

drm/msm: fix use-after-free on probe deferral

The bridge counter was never reset when tearing down the DRM device so that stale pointers to deallocated structures would be accessed on the next tear down (e.g. after a second late bind deferral).

Given enough bridges and a few probe deferrals this could currently also lead to data beyond the bridge array being corrupted.

Patchwork: https://patchwork.freedesktop.org/patch/502665/