migration: fix typos in qapi-schema from latest migration additions

#

# @error-desc: #optional the human readable error description string, when

#              @status is 'failed'. Clients should not attempt to parse the

#              error strings. (Since 2.6)

#              error strings. (Since 2.7)

#

# Since: 0.14.0

##

#             be for a 'client' endpoint, while for the incoming side the

#             credentials must be for a 'server' endpoint. Setting this

#             will enable TLS for all migrations. The default is unset,

#             resulting in unsecured migration at the QEMU level. (Since 2.6)

#             resulting in unsecured migration at the QEMU level. (Since 2.7)

#

# @tls-hostname: hostname of the target host for the migration. This is

#                required when using x509 based TLS credentials and the

#                migration URI does not already include a hostname. For

#                example if using fd: or exec: based migration, the

#                hostname must be provided so that the server's x509

#                certificate identity canbe validated. (Since 2.6)

#                certificate identity can be validated. (Since 2.7)

#

# Since: 2.4

##