Fix kconfig dependency warning by using a different Kconfig symbol.

WARNING: unmet direct dependencies detected for VIRTIO_DMA_SHARED_BUFFER
  Depends on [n]: VIRTIO_MENU [=n] && DMA_SHARED_BUFFER [=y]
  Selected by [y]:
  - DRM_VIRTIO_GPU [=y] && HAS_IOMEM [=y] && DRM [=y] && VIRTIO [=y] && MMU [=y]
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: http://patchwork.freedesktop.org/patch/msgid/7481fb88-6b04-3726-57e0-0f513245c657@infradead.org
Cc: David Airlie <airlied@linux.ie>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>