vhost: (cosmetic) remove a superfluous variable initialisation

Even the compiler is able to figure out that in this case the
initialisation is superfluous.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Link: https://lore.kernel.org/r/20200527180541.5570-3-guennadi.liakhovetski@linux.intel.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>