qemu: avoid 32-bit compiler warning

On 32-bit platforms, gcc warns that the comparison between a long
and (ULLONG_MAX/1024/1024) is always false; throwing in a type
conversion shuts up the warning.

* src/qemu/qemu_monitor.c (qemuMonitorBlockJob): Shut gcc up.

src/qemu/qemu_monitor.c

@@ -2785,7 +2785,7 @@ int qemuMonitorBlockJob(qemuMonitorPtr mon,
               modern);
 
     /* Convert bandwidth MiB to bytes */
-    if (bandwidth > ULLONG_MAX / 1024 / 1024) {
+    if (bandwidth * 1ULL > ULLONG_MAX / 1024 / 1024) {
         qemuReportError(VIR_ERR_OVERFLOW,
                         _("bandwidth must be less than %llu"),
                         ULLONG_MAX / 1024 / 1024);