drm/amd/amdgpu/amdgpu_vm_pt: Supply description for amdgpu_vm_pt_free_dfs()'s unlocked param

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c:683: warning: Function parameter or member 'unlocked' not described in 'amdgpu_vm_pt_free_dfs'

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c

@@ -673,6 +673,7 @@ void amdgpu_vm_pt_free_work(struct work_struct *work)
  * @adev: amdgpu device structure
  * @vm: amdgpu vm structure
  * @start: optional cursor where to start freeing PDs/PTs
+ * @unlocked: vm resv unlock status
  *
  * Free the page directory or page table level and all sub levels.
  */