usb: dwc2: gadget: Fix WkupAlert interrupt handler.

According to the databook DCTL_RMTWKUPSIG bit
is defined in DCTL register not in DCFG.

Updated setting DCTL_RMTWKUPSIG bit to DCTL
register.

Fixes: 187c5298

 ("usb: dwc2: gadget: Add handler for WkupAlert interrupt")

Signed-off-by: Artur Petrosyan <arturp@synopsys.com>
Signed-off-by: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>