vhost: fix deadlock when message handling failed

vhost: fix deadlock when message handling failed

In vhost_user_msg_handler(), if vhost message handling
failed, we should check whether the queue is locked and
release the lock before returning. Or, it will cause a
deadlock later.

Fixes: 7f31d4ea05ca ("vhost: fix lock on device readiness notification")
Cc: stable@dpdk.org
Signed-off-by: Wenwu Ma <wenwux.ma@intel.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Tested-by: Wei Ling <weix.ling@intel.com>
Acked-by: David Marchand <david.marchand@redhat.com>