drm/vmwgfx: Fix a sparse warning in kernel docs

Fixes a warning about extra docs about a function argument that has been
removed a while back:
drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c:3888: warning: Excess function
parameter 'sync_file' description in 'vmw_execbuf_copy_fence_user'

Fixes: a0f90c88 ("drm/vmwgfx: Fix stale file descriptors on failed usercopy")
Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Reviewed-by: Maaz Mombasawala <mombasawalam@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221022040236.616490-18-zack@kde.org

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -3869,7 +3869,6 @@ int vmw_execbuf_fence_commands(struct drm_file *file_priv,
  * @fence: Pointer to the fenc object.
  * @fence_handle: User-space fence handle.
  * @out_fence_fd: exported file descriptor for the fence.  -1 if not used
- * @sync_file:  Only used to clean up in case of an error in this function.
  *
  * This function copies fence information to user-space. If copying fails, the
  * user-space struct drm_vmw_fence_rep::error member is hopefully left