drm/vmwgfx: Set surface-framebuffer GEM objects

drm/vmwgfx: Set surface-framebuffer GEM objects

Set struct drm_framebuffer.obj[0] to the allocated GEM buffer object
for surface framebuffers. Avoids a NULL-pointer deref in the client's
vmap helpers.

[   22.640191] Console: switching to colour frame buffer device 160x50
[   22.641788] Oops: general protection fault, probably for
  non-canonical address 0xdffffc000000001f: 0000 [#1] SMP KASAN NOPTI
[   22.641795] KASAN: null-ptr-deref in range
[0x00000000000000f8-0x00000000000000ff]
[...]
[   22.641809] Hardware name: VMware, Inc. VMware20,1/440BX Desktop
  Reference Platform, BIOS VMW201.00V.24928539.B64.2508260915 08/26/2025
[   22.641812] Workqueue: events drm_fb_helper_damage_work
[   22.641824] RIP: 0010:drm_gem_lock+0x25/0x50
[   22.641831] Code: 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 b8
  00 00 00 00 00 fc ff df 53 48 89 fb 48 81 c7 f8 00 00 00 48 89 fa 48
  c1 ea 03 <80> 3c 02 00 75 0f 48 8b bb f8 00 00 00 31 f6 5b e9 16 2e 15
  01 e8
[...]
[   22.641889] Call Trace:
[   22.641891]  <TASK>
[   22.641894]  drm_client_buffer_vmap_local+0x78/0x140
[   22.641903]  drm_fbdev_ttm_helper_fb_dirty+0x20c/0x510 [drm_ttm_helper]
[   22.641913]  ? __pfx_drm_fbdev_ttm_helper_fb_dirty+0x10/0x10 [drm_ttm_helper]
[   22.641918]  ? __raw_spin_lock_irqsave+0x8c/0xf0
[   22.641924]  ? __pfx___raw_spin_lock_irqsave+0x10/0x10
[   22.641928]  ? __pfx_mutex_lock+0x10/0x10
[   22.641936]  drm_fb_helper_fb_dirty+0x29a/0x5e0
[   22.641942]  ? __pfx_drm_fb_helper_fb_dirty+0x10/0x10
[...]

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: ea39f2e66e61 ("drm/client: Deprecate struct drm_client_buffer.gem")
Reported-by: Ian Forbes <ian.forbes@broadcom.com>
Closes: https://lore.kernel.org/dri-devel/CAO6MGtjg8PiRiSLomJQRBduTBSC0WkqX67tEZwA9qwOgRzchpw@mail.gmail.com/
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Tested-by: Ian Forbes <ian.forbes@broadcom.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patch.msgid.link/20251104103611.167821-1-tzimmermann@suse.de