usb: dwc2: gadget: Corrected interval calculation

Calculate the interval according to the USB 2.0 specification section
9.6.6.

Tested-by: John Keeping <john@metanate.com>
Signed-off-by: Vardan Mikayelyan <mvardan@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
index 5516099..0ba3599 100644
--- a/drivers/usb/dwc2/core.h
+++ b/drivers/usb/dwc2/core.h
@@ -166,7 +166,7 @@
  *          means that it is sending data to the Host.
  * @index: The index for the endpoint registers.
  * @mc: Multi Count - number of transactions per microframe
- * @interval - Interval for periodic endpoints
+ * @interval - Interval for periodic endpoints, in frames or microframes.
  * @name: The name array passed to the USB core.
  * @halted: Set if the endpoint has been halted.
  * @periodic: Set if this is a periodic ep, such as Interrupt