drm/v3d: Fix global performance monitor reference counting

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

drm/v3d: Fix global performance monitor reference counting

In the SET_GLOBAL ioctl, v3d_perfmon_find() bumps the reference count on

the perfmon it returns, but v3d_perfmon_set_global_ioctl() and

v3d_perfmon_delete() fail to release that reference on several paths:

1. v3d_perfmon_set_global_ioctl() leaks the reference on its error

paths.

2. CLEAR_GLOBAL leaks both the find reference and the reference

previously stashed in v3d->global_perfmon by the SET_GLOBAL ioctl

that configured it.

3. Destroying a perfmon that is the current global perfmon leaks the

reference stashed by the SET_GLOBAL ioctl.

Release each of these references explicitly.