usb: dwc2: gadget: Remove unnecessary code

This chunk is not needed here. There is no functionality
depend on this, so if no-op, I think we do not need to have
this interrupt unmasked.

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>