usb: dwc3: core: don't forget to free coherent memory

commit 3921426b (usb: dwc3: core: move
event buffer allocation out of
dwc3_core_init()) introduced a memory leak
of the coherent memory we use as event
buffers on dwc3 driver.

If the driver is compiled as a dynamically
loadable module and use constantly loads
and unloads the driver, we will continue
to leak the coherent memory allocated during
->probe() because dwc3_free_event_buffers()
is never called during ->remove().

Cc: <stable@vger.kernel.org> # v3.7 v3.8
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/core.c

@@ -583,6 +583,7 @@ static int dwc3_remove(struct platform_device *pdev)
 		break;
 	}
 
+	dwc3_free_event_buffers(dwc);
 	dwc3_core_exit(dwc);
 
 	return 0;