qemu-nbd: drop loop which can never loop

For some reason nbd_client_thread() has a do..while loop which can never
loop, the condition is bogus because we would take a goto instead.  Drop
the loop.

Reported-by: Dr David Alan Gilbert <davidagilbert@uk.ibm.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

qemu-nbd.c

@@ -202,12 +202,10 @@ static void *nbd_client_thread(void *arg)
     int ret;
     pthread_t show_parts_thread;
 
-    do {
-        sock = unix_socket_outgoing(sockpath);
-        if (sock == -1) {
-            goto out;
-        }
-    } while (sock == -1);
+    sock = unix_socket_outgoing(sockpath);
+    if (sock == -1) {
+        goto out;
+    }
 
     ret = nbd_receive_negotiate(sock, NULL, &nbdflags,
                                 &size, &blocksize);