io: fix sign of errno value passed to error report

When reporting the number of FDs has been exceeded, pass
EINVAL to error_setg_errno, rather than -EINVAL.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/io/channel-socket.c b/io/channel-socket.c
index 10a5b31..eaa411f 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -502,7 +502,7 @@
 
     if (nfds) {
         if (nfds > SOCKET_MAX_FDS) {
-            error_setg_errno(errp, -EINVAL,
+            error_setg_errno(errp, EINVAL,
                              "Only %d FDs can be sent, got %zu",
                              SOCKET_MAX_FDS, nfds);
             return -1;