HID: hiddev: fix nonblocking read semantics wrt EIO/ERESTARTSYS

When the file has been open in non-blocking mode, EIO or ERESTARTSYS
would never be returned even if they should (for example when device
has been unplugged, you want EIO and not EAGAIN to be returned).

Move the O_NONBLOCK check after other checks have been performed.

Base on similar patch done to hidraw by
Founder Fang <founder.fang@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/usbhid/hiddev.c

@@ -361,10 +361,6 @@ static ssize_t hiddev_read(struct file * file, char __user * buffer, size_t coun
 			prepare_to_wait(&list->hiddev->wait, &wait, TASK_INTERRUPTIBLE);
 
 			while (list->head == list->tail) {
-				if (file->f_flags & O_NONBLOCK) {
-					retval = -EAGAIN;
-					break;
-				}
 				if (signal_pending(current)) {
 					retval = -ERESTARTSYS;
 					break;
@@ -373,6 +369,10 @@ static ssize_t hiddev_read(struct file * file, char __user * buffer, size_t coun
 					retval = -EIO;
 					break;
 				}
+				if (file->f_flags & O_NONBLOCK) {
+					retval = -EAGAIN;
+					break;
+				}
 
 				/* let O_NONBLOCK tasks run */
 				mutex_unlock(&list->thread_lock);