chardev/tcp: Fix error message double free error

chardev/tcp: Fix error message double free error

Errors are already freed by error_report_err, so we only need to call
error_free when that function is not called.

Cc: qemu-stable@nongnu.org
Signed-off-by: lichun <lichun@ruijie.com.cn>
Message-Id: <20200621213017.17978-1-lichun@ruijie.com.cn>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message improved, cc: qemu-stable]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
(cherry picked from commit ed4e0d2ef140aef255d67eec30767e5fcd949f58)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>