drm/i915/gvt: fix the usage of ww lock in gvt scheduler.

drm/i915/gvt: fix the usage of ww lock in gvt scheduler.

As the APIs related to ww lock in i915 was changed recently, the usage of
ww lock in GVT-g scheduler needs to be changed accrodingly. We noticed a
deadlock when GVT-g scheduler submits the workload to i915. After some
investigation, it seems the way of how to use ww lock APIs has been
changed. Releasing a ww now requires a explicit i915_gem_ww_ctx_fini().

Fixes: 81d4bd453a80 ("drm/i915/gvt: Introduce per object locking in GVT scheduler.")
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhi A Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210826143834.25410-1-zhi.a.wang@intel.com
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>