i2c: viperboard: return message count on master_xfer success

Returning zero is wrong in this case.
Signed-off-by: NPeter Rosin <peda@axentia.se>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>
Fixes: 174a13aa ("i2c: Add viperboard i2c master driver")

drivers/i2c/busses/i2c-viperboard.c

@@ -337,7 +337,7 @@ static int vprbrd_i2c_xfer(struct i2c_adapter *i2c, struct i2c_msg *msgs,
 		}
 		mutex_unlock(&vb->lock);
 	}
-	return 0;
+	return num;
 error:
 	mutex_unlock(&vb->lock);
 	return error;