drm/v3d: Fix global performance monitor reference counting

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.

Cc: stable@vger.kernel.org
Fixes: c6eabbab359c ("drm/v3d: Add DRM_IOCTL_V3D_PERFMON_SET_GLOBAL")
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patch.msgid.link/20260531-v3d-perfmon-lifetime-v2-1-60ed4485a203@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>