vhost: remove unneeded variable assignment
vhost: remove unneeded variable assignment

Found with clang static analysis:
lib/librte_vhost/vhost_user.c:996:3: warning:
Value stored to 'ret' is never read
        ret = vhost_user_get_vring_base(dev, &msg.payload.state);
        ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Emmanuel Roullit <e51ad7dcb99c77ecf30f537962c562ac80636eba@gmail.com>
Acked-by: Yuanhan Liu <5dcef21195e64c9c08aa779bb62b25e9133eaa33@linux.intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk