usb: dwc2: Fixed SOF interrupt enabling/disabling

In case of DDMA mode we don't need to get an SOF interrupt so disable
the unmasking of SOF interrupt in DDMA mode.

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