Poll for migration end every 50ms instead of 50us

The comment in qemuDomainWaitForMigrationComplete says we are polling
every 50ms but the code sleeps only for 50us. This was already discussed
during review but apparently forgotten when the series was pushed.

src/qemu/qemu_driver.c

@@ -4524,7 +4524,7 @@ qemuDomainWaitForMigrationComplete(struct qemud_driver *driver, virDomainObjPtr
 
     while (priv->jobInfo.type == VIR_DOMAIN_JOB_UNBOUNDED) {
         /* Poll every 50ms for progress & to allow cancellation */
-        struct timespec ts = { .tv_sec = 0, .tv_nsec = 50 * 1000ull };
+        struct timespec ts = { .tv_sec = 0, .tv_nsec = 50 * 1000 * 1000ull };
         struct timeval now;
         int rc;