gpu/drm/virtio/virtgpu_vq.c: Use kmem_cache_zalloc

Replaced kmem_cache_alloc + memset with kmem_cache_zalloc

Signed-off-by: Sabyasachi Gupta <sabyasachi.linux@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/5bc9ff7e.1c69fb81.105c2.1fef@mx.google.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>