drm/vmwgfx: fix kernel-doc Excess struct member 'base'

Fix a new kernel-doc warning reported by kernel test robot:

vmwgfx_surface.c:55: warning: Excess struct member 'base' description in 'vmw_user_surface'

The other warning is not correct: it is confused by "__counted_by".
Kees has made a separate patch for that.

In -Wall mode, kernel-doc still reports 20 warnings of this nature:
vmwgfx_surface.c:198: warning: No description found for return value of 'vmw_surface_dma_size'
but I am not addressing those.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312150701.kNI9LuM3-lkp@intel.com/
Cc: Kees Cook <keescook@chromium.org>
Cc: Zack Rusin <zackr@vmware.com>
Cc: VMware Graphics Reviewers <linux-graphics-maintainer@vmware.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231215235638.19189-1-rdunlap@infradead.org

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -44,7 +44,6 @@
  * struct vmw_user_surface - User-space visible surface resource
  *
  * @prime: The TTM prime object.
- * @base: The TTM base object handling user-space visibility.
  * @srf: The surface metadata.
  * @master: Master of the creating client. Used for security check.
  */