cpus: tcg: fix never exiting loop on unplug

Commit 9b0605f9837b ("cpus: tcg: unregister thread with RCU, fix
exiting of loop on unplug") changed the exit condition of the loop in
the vCPU thread function but forgot to remove the beginning 'while (1)'
statement. The resulting code :

	while (1) {
	...
	} while (!cpu->unplug || cpu_can_run(cpu));

is a sequence of two distinct two while() loops, the first not exiting
in case of an unplug event.

Remove the first while (1) to fix CPU unplug.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20180425131828.15604-1-clg@kaod.org>
Cc: qemu-stable@nongnu.org
Fixes: 9b0605f9837b68fd56c7fc7c96a3a1a3b983687d
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

cpus.c

@@ -1648,7 +1648,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
     /* process any pending work */
     cpu->exit_request = 1;
 
-    while (1) {
+    do {
         if (cpu_can_run(cpu)) {
             int r;
             qemu_mutex_unlock_iothread();