tools/virtio: fix build breakage

Previous commit ("virtio: add context flag to find vqs")
added a new 'context' flag to vring_new_virtqueue(), but the
corresponding API in tools/virtio/ is not updated causing
build errors due to conflicting declarations.

Bring code in tools/virtio in sync with that in kernel.

I have used 'false' for the value of the new boolean 'context'
flag as that seems to be the best way to preserve existing
behavior.

Tested with:

$ make -C tools/virtio clean all ARCH=x86

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>