staging: android: logger: reorder prepare_to_wait and mutex_lock

If mutex_lock waits, it will return in state TASK_RUNNING,
rubbing out the effect of prepare_to_wait().
Signed-off-by: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/logger.c

@@ -172,9 +172,10 @@ static ssize_t logger_read(struct file *file, char __user *buf,
 
 start:
 	while (1) {
+		mutex_lock(&log->mutex);
+
 		prepare_to_wait(&log->wq, &wait, TASK_INTERRUPTIBLE);
 
-		mutex_lock(&log->mutex);
 		ret = (log->w_off == reader->r_off);
 		mutex_unlock(&log->mutex);
 		if (!ret)