usb: dwc3: gadget: Fix starting microframe for ISOC

The gadget wants to set the starting microframe for the first ISOC TRB
to 4 microframes in the future, but it does so by multiplying the
dep->interval. This only works if dep->interval = 1. For other intervals
it will put it 4 *intervals* in the future which may be way too much.

Fix so that it always adds just one interval or at least 4 microframes.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -1184,8 +1184,11 @@ static void __dwc3_gadget_start_isoc(struct dwc3 *dwc,
 		return;
 	}
 
-	/* 4 micro frames in the future */
-	uf = cur_uf + dep->interval * 4;
+	/*
+	 * Schedule the first trb for one interval in the future or at
+	 * least 4 microframes.
+	 */
+	uf = cur_uf + max_t(u32, 4, dep->interval);
 
 	__dwc3_gadget_kick_transfer(dep, uf);
 }