Potential memory leak in virtio-crytpto
Description of problem:
There is a potential memory leak while using virtio-crypto with vhost-user backend.

The problem is due to misuse of error_setg in [backends/cryptodev-vhost-user.c#L284](https://gitlab.com/qemu-project/qemu/-/blob/master/backends/cryptodev-vhost-user.c#L284). After invoking error_setg(&local_error, ...), current procedure should not return without freeing err object pointed by local_error.

The same problem occured in cryptodev-builtin, which has been discussed in #2283 and fixed in f6abce29cc4afa0445cb3b29a265a114ac9fa744. The same fixes should be applied to cryptodev-vhost-user.