Update usb.py

Author: pjt0620

openxc/sources/usb.py

@@ -82,7 +82,7 @@ def _read(self, endpoint_address, timeout=None,
             read_size=DEFAULT_READ_REQUEST_SIZE):
         timeout = timeout or self.DEFAULT_READ_TIMEOUT
         try:
-            str(return self.device.read(0x80 + endpoint_address,
+            return str(self.device.read(0x80 + endpoint_address,
                     read_size, self.DEFAULT_INTERFACE_NUMBER, timeout
                     ),'utf-8')
         except (usb.core.USBError, AttributeError) as e: