drm/v3d: Stop active perfmon if it is being destroyed

In the Linux kernel, the following vulnerability has been resolved: drm/v3d: Stop active perfmon if it is being destroyed If the active performance monitor (`v3d->active_perfmon`) is being destroyed, stop it first. Currently, the active perfmon is not stopped during destruction, leaving the `v3d->active_perfmon` pointer stale. This can lead to undefined behavior and instability. This patch ensures that the active perfmon is stopped before being destroyed, aligning with the behavior introduced in commit 7d1fd3638ee3 ("drm/v3d: Stop the active perfmon before being destroyed").