vhost: remove fallback in async enqueue API
vhost: remove fallback in async enqueue API

By design, async enqueue API should return directly if async device
is not registered. This patch removes the corrupted implementation of
the enqueue fallback from async mode to sync mode.

Fixes: cd6760da1076 ("vhost: introduce async enqueue for split ring")
Cc: stable@dpdk.org

Signed-off-by: Patrick Fu <9a0e5a62d6df51dec9c1e0dc80b22878833f5aba@intel.com>
Reviewed-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>

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