qemu-ga: Plug fd leak on ga_channel_open() error paths

Spotted by Coverity.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qga/channel-posix.c

@@ -154,6 +154,7 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path, GAChannelMethod
         ret = ga_channel_client_add(c, fd);
         if (ret) {
             g_critical("error adding channel to main loop");
+            close(fd);
             return false;
         }
         break;