HID: fix possible deadlock in hidraw_read

If the loop in hidraw_read() loops more than once, then we might
end up trying to acquire already locked mutex, casuing a deadlock.
Reported-by: iceberg <iceberg@ispras.ru>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hidraw.c

@@ -47,10 +47,9 @@ static ssize_t hidraw_read(struct file *file, char __user *buffer, size_t count,
 	char *report;
 	DECLARE_WAITQUEUE(wait, current);
 
-	while (ret == 0) {
-
 	mutex_lock(&list->read_mutex);
 
+	while (ret == 0) {
 		if (list->head == list->tail) {
 			add_wait_queue(&list->hidraw->wait, &wait);
 			set_current_state(TASK_INTERRUPTIBLE);